EPA/630/R-03/003F 

March 2005

Supplemental Guidance for Assessing Susceptibility from 

Early-Life Exposure to Carcinogens 

Risk Assessment Forum 

U.S. Environmental Protection Agency 

Washington, DC 20460 

 
DISCLAIMER

 This document has been reviewed in accordance with U.S. Environmental Protection

Agency policy and approved for publication. Mention of trade names or commercial products 

does not constitute endorsement or recommendation for use.

 ii 
AUTHORS AND CONTRIBUTORS

This document was prepared by a Technical Panel of the Risk Assessment Forum.

AUTHORS

 

Hugh Barton, National Health and Environmental Effects Research Laboratory, ORD 

Jim Cogliano, National Center for Environmental Assessment, ORD 

Michael P. Firestone, Office of Children's Health Protection, OA

Lynn Flowers, National Center for Environmental Assessment, ORD 

R. Woodrow Setzer, National Health and Environmental Effects Research Laboratory, 

ORD 

Larry Valcovic, National Center for Environmental Assessment, ORD 

Tracey Woodruff, Office of Policy, Economics, and Innovation, OA 

CONTRIBUTORS 

Neepa Choksi, Fellow to the Office of Solid Waste and Emergency Response 

Resha M. Putzrath, Risk Assessment Forum Staff, National Center for Environmental 

Assessment, ORD 

William P. Wood, Risk Assessment Forum Staff, National Center for Environmental, ORD 

 iii
ACKNOWLEDGMENTS 

We would especially like to thank David Bennett for his earlier work in leading the initial 

efforts for this work, Bill Wood for his support, and Julian Preston for his helpful review of the 

document. Special thanks also go to Rebecca Brown, Rosemary Castorina, Ellen Phelps, and 

Linda Poore for their efforts in pulling together the underlying information. 

 iv
CONTENTS

PREFACE.......................................................................................................................................vi

1. INTRODUCTION .............................................................................................................................. 1

2. PROCEDURES ................................................................................................................................. 6 

2.1. DATA SOURCES FOR ANIMAL STUDIES ................................................................... 6 

2.2. EVALUATING THE MODE OF ACTION OF CARCINOGENS ................................... 8 

2.3. QUANTITATIVE METHODS .......................................................................................... 9 

2.4. IONIZING RADIATION ................................................................................................. 12 

3. RESULTS ...................................................................................................................................... 13 

3.1. QUALITATIVE EVALUATION OF THE DATABASE ............................................... 13 

3.2. QUANTITATIVE EVALUATION OF THE DATABASE ............................................ 15 

3.2.1. Carcinogens with a Mutagenic Mode of Action........................................................ 16 

3.2.1.1. Early Postnatal, Juvenile, and Adult Repeated Dosing Studies of Chemicals 

with a Mutagenic Mode of Action......................................................................... 16 

3.2.1.2. Acute Dosing Studies of Chemicals with a Mutagenic Mode of Action........ 17 

3.2.2. Carcinogens with Modes of Action Other Than Mutagenicity.................................. 19 

3.2.3. Ionizing Radiation...................................................................................................... 21 

4. DISCUSSION ................................................................................................................................. 23 

5. GUIDANCE FOR ASSESSING CANCER RISKS FROM EARLY-LIFE EXPOSURE .................................... 30 

6. COMBINING LIFESTAGE DIFFERENCES IN EXPOSURE AND DOSE-RESPONSE WHEN ASSESSING 

CARCINOGEN RISK - SOME EXAMPLES FOR CARCINOGENS THAT ACT THROUGH A MUTAGENIC 

MODE OF ACTION........................................................................................................................ 36

 6.1 CALCULATING LIFETIME RISKS ASSOCIATED WITH LIFETIME EXPOSURES ........................... 36

 6.2 CALCULATING LIFETIME RISKS ASSOCIATED WITH LESS THAN LIFETIME EXPOSURES....... 368

APPENDIX A: TABLES ................................................................................................................... A-1 

Table 1a. Chemicals that have been found to have carcinogenic effects from prenatal or postnatal 

exposure in animals as identified in different review articles........................................A-1 

Table 1b. List of chemicals considered in this analysis. (These are chemicals for which there are 

both early-life and adult exposure reported in the same animal experiment.)......... ...........A-3 

Table 2. Methodological information and tumor incidence for animal studies with early 

postnatal and juvenile and adult repeated exposures..................................................A-5 

Table 3. Methodological information and tumor incidence for animal studies with early 

postnatal and juvenile and adult acute exposure...................................................A-17 

Table 4. Ratio of early-life to adult cancer potencies for studies with repeated exposures of 

juvenile and adult animals to carcinogens with a mutagenic mode of action.....................A-44 

Table 5: Ratio of early-life to adult cancer potencies for studies with repeated exposures of 

juvenile and adult animals to chemicals with other than mutagenic modes of action.......A-45 

 v
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of 

juveniles and adult animals to chemicals with mutagenic modes of action.....................A-46 

Table 7. Ratio of early-life to adult cancer potencies for studies with lifetime exposures starting 

with juvenile and adult...................................................................................A-57 

Table 8. Summary of quantitative estimates of ratio of early-life to adult cancer 

potencies...................................................................................................A-60 

Table 9. Excess Relative Risk (ERR) estimates for cancer incidence from Life Span Study 

(Japanese survivors)......................................................................................A-61 

Table 10. Excess Relative Risk estimates for incidence of thyroid cancer from Life Span 

Study........................................................................................................A-62 

Table 11. Coefficients for the Revised Methodology mortality risk model (from U.S. EPA, 

1999)........................................................................................................A-63 

REFERENCES ................................................................................................................................... R-1 

LIST OF FIGURES 

Figure 1. Flow chart for early-life risk assessment using mode of action framework ............... 42 

Figure 2. Posterior, unweighted geometric means and 95% confidence intervals for the ratios of 

juvenile to adult cancer potency for carcinogens acting primarily through a mutagenic 

mode of action............................................................................................................. 43 

Figure 3. Study designs.............................................................................................................. 44 

 vi
PREFACE

U.S. Environmental Protection Agency (EPA or the Agency) cancer risk assessments 

may be conducted differently than envisioned in this Supplemental Guidance for many reasons 

including, for example, new information, new scientific understanding, or different science 

policy judgment. The practice of risk assessment with respect to accounting for early-life 

exposures to toxicants continues to develop, and specific components of this Supplemental 

Guidance may become outdated or may otherwise require modification in individual settings. It 

is EPA’s intent to use, to the extent practicable and consistent with Agency statutes and 

regulations, the best available science in its risk assessments and regulatory actions, and this 

Supplemental Guidance is not intended to provide any substantive or procedural obstacle in 

achieving that goal. Therefore, the Supplemental Guidance has no binding effect on EPA or on 

any regulated entity. Where EPA does use the approaches in the Supplemental Guidance in 

developing risk assessments, it will be because EPA has decided in the context of that risk 

assessment that the approaches from the Supplemental Guidance are suitable and appropriate. 

This judgment will be tested through peer review, and the risk assessment will be modified to 

use different approaches if appropriate. 

This Supplemental Guidance is intended for guidance only. It does not establish any 

substantive “rules” under the Administrative Procedure Act or any other law and has no binding 

effect on EPA or any regulated entity, but instead represents a non-binding statement of policy. 

The Supplemental Guidance addresses a number of issues pertaining to cancer risks 

associated with early-life exposures generally, but provides specific guidance on potency 

adjustment only for carcinogens acting through a mutagenic mode of action. This guidance 

recommends for such chemicals, a default approach using estimates from chronic studies (i.e., 

cancer slope factors) with appropriate modifications to address the potential for differential risk 

of early-lifestage exposure. Default adjustment factors are meant to be used only when no 

chemical-specific data are available to assess directly cancer susceptibility from early-life 

exposure to a carcinogen acting through a mutagenic mode of action.

The Agency considered both the advantages and disadvantages of extending the 

recommended, age dependent adjustment factors for carcinogenic potency to carcinogenic agents 

for which the mode of action remains unknown. EPA recommends these factors only for 

carcinogens acting through a mutagenic mode of action based on a combination of analysis of 

available data and long-standing science policy positions that set out the Agency’s overall 

approach to carcinogen risk assessment, e.g., the use of a linear, no threshold extrapolation 

procedure in the absence of data in order to be health protective. In general, the Agency prefers 

 vii
to rely on analyses of data rather than on general defaults. When data are available for a 

susceptible lifestage, they should be used directly to evaluate risks for that chemical and that 

lifestage on a case-by-case basis. In the case of nonmutagenic carcinogens, when the mode of 

action is unknown, the data were judged by EPA to be too limited and the modes of action too 

diverse to use this as a category for which a general default adjustment factor approach can be 

applied. In this situation per the Agency’s Guidelines for Carcinogen Risk Assessment, a linear 

low-dose extrapolation methodology is recommended. It is the Agency’s long-standing science 

policy position that use of the linear low-dose extrapolation approach (without further 

adjustment) provides adequate public health conservatism in the absence of chemical-specific 

data indicating differential early-life susceptibility or when the mode of action is not 

mutagenicity. 

The Agency expects to produce additional supplemental guidance for other modes of 

action, as data from new research and toxicity testing indicate it is warranted. EPA intends to 

focus its research, and to work collaboratively with its federal partners, to improve understanding 

of the implications of early life exposure to carcinogens. Development of guidance for 

estrogenic agents and chemicals acting through other processes resulting in endocrine disruption 

and subsequent carcinogenesis, for example, might be a reasonable priority in light of the human 

experience with diethylstilbesterol and the existing early-life animal studies. It is worth noting 

that each mode of action for endocrine disruption will probably require separate analysis. 

As the Agency examines additional carcinogenic agents, the age groupings may differ 

from those recommended for assessing cancer risks from early-life exposure to chemicals with a 

mutagenic mode of action. Puberty and its associated biological changes, for example, involve 

many biological processes that could lead to changes in susceptibility to the effects of some

carcinogens, depending on their mode of action. The Agency is interested in identifying 

lifestages that may be particularly sensitive or refractory for carcinogenesis, and believes that the 

mode of action framework described in the Agency’s Guidelines for Carcinogen Risk 

Assessment is an appropriate mechanism for elucidating these lifestages. For each additional 

mode of action evaluated, the various age groupings determined to be at differential risk may 

differ from those described in this Supplemental Guidance. For example, the age groupings 

selected for the age-dependent adjustments were initially selected based on the available data, 

i.e., for the laboratory animal age range representative of birth to < 2 years in humans. More 

limited data and information on human biology are being used to determine a science-informed 

policy regarding 2 to < 16 years. Data were not available to refine the latter age group. If more 

data become available regarding carcinogens with a mutagenic mode of action, consideration 

may be given to further refinement of these age groups. 

 viii
Access to data and other information relating to the Cancer Guidelines (U.S. EPA, 2005) 

and this Supplemental Guidance will be through EPA's Risk Assessment Forum website, under 

Publications, Guidelines, Guidelines for Cancer Risk Assessment. The URL is 

http://www.epa.gov/cancerguidelines. The data and results of analyses are available in 

spreadsheets.

 ix
1. INTRODUCTION 

Cancer risk to children in the context of the U.S. Environmental Protection Agency’s 

cancer guidelines (U.S. EPA, 2005) includes both early-life exposures that may result in the 

occurrence of cancer during childhood and early-life exposures that may contribute to cancers 

later in life. The National Research Council (NRC, 1994) recommended that “EPA should 

assess risks to infants and children whenever it appears that their risks might be greater than 

those of adults.” This document focuses on cancer risks from early-life exposure compared with 

those from exposures occurring later in life. Evaluating childhood cancer and childhood 

exposures resulting in cancer later in life are related, but separable, issues.

Historically, the focus on cancer has been as a disease associated with aging, resulting 

from extended exposure duration with prolonged latency periods before the cancers appear. 

Because much of cancer epidemiology addresses occupational exposures and because rodent 

cancer studies are designed to last approximately a lifetime (two years) beginning after sexual 

maturity, the cancer database used by EPA and other agencies for risk assessment focuses on 

adults. However, extensive literature demonstrates that exposures early in life (i.e., 

transplacental or in utero, early postnatal, lactational) in animals can result in the development of 

cancer (reviewed in Toth, 1968; Della Porta and Terracini, 1969; Druckery, 1973; Rice, 1979; 

Vesselinovitch et al., 1979; Rice and Ward, 1982; Vesselovitch et al., 1983; Anderson et al., 

2000). Thus, one element in extending analyses to children is to evaluate the extent to which 

exposures early in life would alter the incidence of cancers observed later in life, compared with 

the incidence observed with adult-only exposures (Anderson et al., 2000; NRC, 1993). 

The causes of cancer encompass a variety of possible risk factors, including genetic 

predisposition (Tomlinson et al., 1997), diet, lifestyle, associations with congenital 

malformations (Bosland, 1996), and exposure to biological and physical agents and chemicals in 

the environment. In some cases, tumors in adults and children have been compared (Anderson et 

al., 2000; Ginsberg et al., 2002). Children and adults generally develop the same spectrum of 

tumors when they have inherited gene and chromosomal mutations, such as Li-Fraumeni 

syndrome (Birch et al., 1998). With ionizing radiation, which operates through a mutagenic 

mode of action, both the young and the old develop many of the same tumors, with the 

difference being that children are more susceptible for a number of tumor types (NRC, 1990; 

U.S. EPA, 1994; UNSCEAR, 2000). Studies with anticancer drugs (cytotoxic and 

immunosuppressive) demonstrate a similar spectrum of tumors (Hale et al., 1999; Kushner et al., 

1998; Larson et al., 1996; Nyandoto et al., 1998). Various viral infections, such as Epstein Barr 

and hepatitis B, lead to lymphoma and liver cancer, respectively, in both age groups (Lindahl et 

 1
al., 1974; Mahoney, 1999). These observations in humans indicate that the mode of action for 

these agents would be the same or similar for adults and children. 

Although there are similarities between childhood and adult tumors, significant 

differences are also known to exist (Grufferman, 1998; Israel, 1995). Tumors of childhood 

generally consist more of embryonic cell tumors, while adults have more carcinomas. 

Leukemias, brain and other nervous system tumors, lymphomas (lymph node cancers), bone 

cancers, soft tissue sarcomas, kidney cancers, eye cancers, and adrenal gland cancers are the 

most common cancers of children, while skin, prostate, breast, lung, and colorectal cancers are 

the most common in adults (Ries et al., 1999; U. S. Cancer Statistics Working Group, 2002). 

Some tumors are unique to the young, including several with well established genetic bases, such 

as tumors of the kidney (Wilms’ tumor) or eye (retinoblastoma) (Anderson et al., 2000; Israel, 

1995). 

The relative rarity in the incidence of childhood cancers and a lack of animal testing 

guidelines with perinatal1

 exposure impede a full assessment of children’s cancer risks from

exposure to chemicals in the environment. Unequivocal evidence of childhood cancer in humans 

occurring from chemical exposures is limited (Anderson et al., 2000). Established risk factors 

for the development of childhood cancer include radiation and certain pharmaceutical agents 

used in chemotherapy (Reise, 1999). There is some evidence in humans for adult tumors 

resulting from perinatal exposure. Pharmacological use of diethylstilbesterol (DES) during 

pregnancy to prevent miscarriages induced clear cell adenocarcinoma of the vagina in a few 

daughters exposed in utero though this tumor was not observed in exposed mothers (Hatch et al., 

1998; Robboy et al., 1984; Vessey, 1989). In addition to the limited human data, there are 

examples of transplacental carcinogens in animal studies, such as recent studies with nickel and 

arsenic (Diwan et al., 1992; Waalkes et al., 2003), as well as studies suggesting that altered 

development can affect later susceptibility2

 to cancer induced by exposure to other chemicals 

(Anderson et al., 2000; Birnbaum and Fenton, 2003). 

Infrequently, perinatal exposure in animals has been shown to induce tumors of different 

types than those observed with adult exposures. Studies with saccharin (Cohen et al., 1995; 

Whysner and Williams, 1996; IARC, 1999) and ascorbate (Cohen et al., 1998; Cohen et al., 

1995; NTP, 1983) found cancer when exposures were initiated in the perinatal period. In 

 1

 Perinatal is defined as the time around birth and may include both prenatal (prior to birth) and postnatal

(after birth) periods. 2

 Susceptibility is defined here as an increased likelihood of an adverse effect, often discussed in terms of

relationship to a factor that can be used to describe a human subpopulation (e.g., lifestage, demographic feature, or

genetic characteristic). The terms “susceptibility” and “sensitivity” are used with a variety of definitions in

published literature making it essential that readers are aware of these differences in terminology across documents. 

 2
contrast, studies submitted to the Food and Drug Administration of approximately a dozen other 

food additives and colorings that were not adult carcinogens did not indicate cancer, even when 

perinatal exposures occurred (U.S. EPA, 1996). When observed, the differences between 

childhood and adult cancers suggest the importance of evaluating the impacts of maternal 

exposures during pregnancy as well as exposures to children (Anderson et al., 2000). The effects 

of maternal exposures and transplacental carcinogens require separate evaluation and are not 

quantitatively evaluated in the analysis presented below. 

The limited human information described briefly above is supported by a number of 

animal bioassays that include both perinatal and adult exposures to chemicals. Standard animal 

bioassays generally begin dosing after the animals are 6-8 weeks old, when many organs and 

systems are almost fully developed, though substantial growth in body size continues thereafter 

(as more fully discussed in Hattis et al., 2005). The literature can be divided roughly into three 

types of exposure scenarios: those that include repeated exposures for the early postnatal to 

juvenile period, as compared with chronic later-life dosing; lifetime (i.e., combined perinatal and 

adult) exposure as compared with chronic later-life dosing; and those that include more acute

exposures, such as a single intraperitoneal (ip) or subcutaneous injection, for both early-life and 

later-life dosing. In the early-life exposure studies that are available, perinatal exposure usually 

induces higher incidence of tumors later in life than the incidence seen in standard bioassays 

where adult animals only were exposed; some examples include diethylnitrosamine (DEN) (Peto 

et al., 1984), benzidine (Vesselinovitch et al., 1979), DDT (Vesselinovitch et al., 1979), and 

polybrominated biphenyls (PCBs) (Chhabra et al., 1993a). Reviews comparing early-life 

carcinogenesis bioassays with standard bioassays for a limited number of chemicals (McConnell, 

1992; Miller et al., 2002; U.S. EPA, 1996) have concluded: 

• The same tumor sites usually are observed following either perinatal or adult exposure. 

• Perinatal exposure in conjunction with adult exposure usually increases the incidence of 

tumor bearing animals or reduces the latent period before tumors are observed. 

There is limited evidence to inform the mode(s) of action leading to differences in tumor 

type and tumor incidence following early-life exposure and exposure later in life. Differences in 

the capacity to metabolize and clear chemicals at different ages can result in larger or smaller 

internal doses of the active agent(s), either increasing or decreasing risk (Ginsberg et al., 2002; 

Renwick, 1998). There is reason to surmise that some chemicals with a mutagenic mode of 

action, which would be expected to cause irreversible changes to DNA, would exhibit a greater 

effect in early-life versus later-life exposure. Several studies have shown increased susceptibility 

 3
of weanling animals to the formation of DNA adducts following exposure to vinyl chloride (Laib 

et al., 1989; Morinello et al., 2002a; Morinello et al., 2002b). Additionally, even though not used 

quantitatively in the analyses in this document, a recent analysis of in vivo transplacental 

micronucleus assays indicated that fetal tissues generally are more sensitive than maternal tissues 

for induction of micronuclei from mutagenic chemicals (Hayashi et al., 2000), providing 

qualitative support for the early-life susceptibility. Similarly, the neonatal mouse model for 

carcinogenesis, which uses two doses prior to weaning followed by observation of tumors at one 

year, shows carcinogenic responses for mutagenic agents (Flammang et al., 1997; McClain et al., 

2001). These results are consistent with the current understanding of biological processes 

involved in carcinogenesis, which leads to a reasonable expectation that children can be more 

susceptible to carcinogenic agents than adults (Anderson et al., 2000; Birnbaum and Fenton, 

2003; Ginsberg, 2003; Miller et al., 2002; Scheuplein et al., 2002). Some aspects potentially 

leading to childhood susceptibility include the following issues. 

• More frequent cell division during development can result in enhanced fixation of 

mutations due to the reduced time available for repair of DNA lesions and clonal 

expansion of mutant cells gives a larger population of mutants (Slikker et al, 2004). 

• Some embryonic cells, such as brain cells, lack key DNA repair enzymes.

• Some components of the immune system are not fully functional during development 

(Holladay and Smialowicz, 2000; Holsapple et al., 2003). 

• Hormonal systems operate at different levels during different lifestages (Anderson et al., 

2000). 

• Induction of developmental abnormalities can result in a predisposition to carcinogenic 

effects later in life (Anderson et al., 2000; Birnbaum and Fenton, 2003; Fenton and 

Davis, 2002). 

The methodology that has been generally used by the U.S. EPA to estimate cancer risk 

associated with oral exposures relies on estimation of the lifetime average daily dose, which can 

account for differences between adults and children with respect to exposure factors such as 

eating habits and body weight. However, susceptibility differences with respect to early 

lifestages are not taken into consideration because cancer slope factors3

 are based upon effects 

 3 Cancer slope factor – An upper bound estimate of the increased cancer risk from a lifetime exposure to an 

agent. This estimate, usually expressed in units of proportion (of a population) affected per unit exposure (e.g.,

mg/kg-day or ug/m3

), is generally reserved for use in the low-dose region of the dose-response relationship. It is

often the statistical upper bound on the potency and therefore the risk. “Upper bound” in this context is a plausible 

 4
observed following exposures to adult humans or sexually mature animals. Since a much larger 

database exists for chemicals inducing cancer in adult humans or sexually mature animals, it is 

necessary to determine whether adjustment of such adult-based cancer slope factors would be 

appropriate when assessing cancer risks associated with exposures early in life. The analysis 

undertaken here addresses this issue, focusing upon studies that define the potential duration and 

degree of increased susceptibility that may arise from childhood, defined as early-life (typically 

postnatal and juvenile animal) exposures. Some of these analyses, along with a more complete 

description of the procedures used, have been published (Barton et al., 2005). The analysis 

presented in this Supplemental Guidance and in the published article form the basis for 

developing Supplemental Guidance for evaluating cancer susceptibility associated with early-life 

exposures. 

 upper limit to the true probability. 

 5
2. PROCEDURES 

This section describes the steps taken to assess potential susceptibility to early-life 

exposure to carcinogenic compounds compared with adult and whole-life exposure. The readily 

available literature was reviewed to identify animal studies that compared tumor incidence 

between early-life and adult-only exposures or between early-life-and-adult and adult-only 

exposures. Studies were categorized by length of exposure; those studies with quantitative 

information to estimate tumor incidence over time for early-life and adult exposures were 

identified. These studies provided the basis for quantitatively estimating the difference in 

susceptibility between early-life and adult exposures, as described below. Finally, summaries of 

available human data for radiation exposure were reviewed in the context of tumor incidence 

from early-life versus later-in-life exposure. 

2.1. DATA SOURCES FOR ANIMAL STUDIES 

Studies in the literature included in this analysis are those that report tumor response from

experiments that included both early-life and adult exposure as separate experimental groups. 

Initial studies for consideration were identified through review articles and a search of the 

National Toxicology Program (NTP) database. Reviews of the literature regarding cancer 

susceptibility from early-life exposure in animals include McConnell (1992), Ginsberg (2003), 

Anderson et al. (2000), Miller et al. (2002) and U.S. EPA (1996). A literature search was 

conducted utilizing key words and MeSH headings (Medline) from studies identified in the 

available reviews. The list of chemicals included in this analysis for quantitative evaluation is 

shown in Table 1a and 1b. 

Abstracts or papers were reviewed to determine if a study provided information that 

could be used for quantitative analysis. The criteria used to decide if a study could be included 

in the quantitative analysis were: 

• Exposure groups at different post-natal ages in the same study or same laboratory, if not 

concurrent (to control for a large number of potential cross-laboratory experimental 

variables including pathological examinations), 

• Same strain/species (to eliminate strain-specific responses confounding age-dependent 

responses), 

• Approximately the same dose within the limits of diets and drinking water intakes that 

obviously can vary with age (to eliminate dose-dependent responses confounding agedependent responses), 

 6
• Similar latency period following exposures of different ages (to control for confounding 

latency period for tumor expression with age-dependent responses), arising from sacrifice 

at >1 year for all groups exposed at different ages, where early-life exposure can occur up 

to about 7 weeks. Variations of around 10 to 20% in latency period are acceptable, 

• Postnatal exposure for juvenile rats and mice at ages younger than the standard 6 to 8 

week start for bioassays; prenatal (in utero) exposures are not part of the current analysis. 

Studies that have postnatal exposure were included (without adjustment) even if they also 

involved prenatal exposure, 

• “Adult” rats and mice exposure beginning at approximately 6 to 8 weeks old or older, i.e. 

comparable to the age at initiation of a standard cancer bioassay (McConnell, 1992). 

Studies with animals only at young ages do not provide appropriate comparisons to 

evaluate age-dependency of response (e.g., the many neonatal mouse cancer studies). 

Studies in other species were used a supporting evidence, because they are relatively rare 

and the determination of the appropriate comparison ages across species is not simple, 

and 

• Number of affected animals and total number of animals examined are available or

reasonably reconstructed for control, young, and adult groups (i.e., studies reporting only 

percent response or not including a control group would be excluded unless a reasonable 

estimate of historical background for the strain was obtainable). 

Tables 2 and 3 include information on the methods and results from the animal studies 

identified in Table 1b. Pertinent information on species, sex, dosing regimen, and tumor 

incidence is given. Additionally, the “Notes” column includes general information about the 

relationship between tumor incidence, animal age at first dosing, and sex. The data in Tables 2 

and 3 were used for the calculations, described below, for estimating potentially increased cancer 

risk from early-life exposure. 

The available literature includes a wide range of exposure scenarios. This range is due in 

part to the lack of a defined protocol for early-life testing and the difficulty of standardizing and 

administering doses preweaning. As noted previously, the literature can be divided roughly into 

three types of exposure scenarios: those that include repeated exposures for the early postnatal to 

juvenile period, as compared with chronic later-life dosing; lifetime (i.e., combined perinatal and 

adult) exposure as compared with chronic later-life dosing; and those that include more acute 

exposures, such as a single intraperitoneal (ip) or subcutaneous injection, for both early-life and 

later-life dosing. Table 2 includes the studies that had early postnatal to juvenile exposures, adult 

chronic exposures, and lifetime exposures. Table 3 includes studies with acute exposures. A 

discussion of the implications of the different exposure scenarios is included in Section 3. 

 7
Studies were identified for more than 50 chemicals not included in Tables 2 and 3 that 

demonstrated carcinogenesis following perinatal exposure, but did not directly compare 

exposures at different ages. A large number of studies address in utero exposures only. More 

than 100 chemicals (with both negative and positive findings) have been studied in the neonatal 

mouse assay, but this assay does not have a comparable adult exposure (Flammang et al., 1997; 

McClain et al., 2001; Fujii, 1991). Studies across laboratories often varied in their use of animal 

strains (e.g., for AZT studies, Diwan et al., 1999 used CD-1 mice, while NTP, 1999 used 

B6C3F1 mice). Studies of tamoxifen use two Wistar-derived strains and had very different 

periods for tumor expression, i.e., sacrifice at 20 months for adult-exposed rats and natural death 

up to 35 months for juvenile-exposed rats, with uterine tumors observed in animals dying after 

22 months (Carthew et al., 2000; Carthew et al., 1996; Carthew et al., 1995). Due to these 

factors, the chemicals that belong to this group were not evaluated quantitatively. In addition, 

there were studies assessing radiation in animals (Covelli et al., 1984; Di et al., 1990; Sasaki et 

al., 1978). The radiation data were not analyzed in depth, in part because there are recognized 

differences in toxicokinetics and toxicodynamics between radiation and chemicals with a 

mutagenic mode of action for carcinogenesis. Even though the data on A-bomb survivors 

provide information for many different cancer sites in humans with a single exposure involving 

all ages, a number of national and international committees of experts have analyzed and 

modeled these data to develop risk estimates for various specific applications. Furthermore, lack 

of uniformity regarding radiation doses, gestational age at exposure, and the animal strains used 

make it difficult to make comparisons across studies (Preston et al., 2000). 

2.2. EVALUATING THE MODE OF ACTION OF CARCINOGENS 

Evaluation of the mode of action of a carcinogen was based upon a weight-of-evidence 

approach. Multiple modes of action are associated with the chemicals in this database, but a 

number are associated with mutagenicity (i.e., benzo(a)pyrene, benzidine, dibenzanthracene, 

diethylnitrosamine, dimethylbenz(a)anthracene, dimethylnitrosamine, ethylnitrosourea, 3-

methylcholanthrene, methylnitrosourea, safrole, urethane, and vinyl chloride). Determination of 

carcinogens that are operating by a mutagenic mode of action entails evaluation of short-term

testing results for genetic endpoints, metabolic profiles, physicochemical properties, and 

structure-activity relationship (SAR) analyses in a weight-of-evidence approach (Dearfield et al., 

1991; U.S. EPA, 1986, 1991; Waters et al., 1999), as has been done for several chemicals (e.g., 

Dearfield et al., 1999; McCarroll et al., 2002; U.S. EPA, 2000a). Key data for a mutagenic mode 

of action may be evidence that the carcinogen or a metabolite is DNA reactive and/or has the 

ability to bind to DNA. Also, such carcinogens usually produce positive effects in multiple test 

 8
systems for different genetic endpoints, particularly gene mutations and structural chromosome

aberrations, and in tests performed in vivo which generally are supported by positive tests in 

vitro. Additionally, carcinogens may be identified as operating via a mutagenic mode of action 

if they have similar properties and SAR to established mutagenic mode of action. 

2.3. QUANTITATIVE METHODS 

To estimate the potential difference in susceptibility between early-life and adult 

exposure, we calculated the estimated ratio of the cancer potency from early-life exposure 

compared to the estimated cancer potency from adult exposure. The cancer potency was 

estimated from a one-hit model, or a restricted form of the Weibull model, which is commonly 

used to estimate cumulative incidence for tumor onset. The general form of the equation is: 

P(dose) = 1-[1-P(0)]exp(-cancer potency*dose) 

 

The ratio of juvenile to adult cancer potencies were calculated by fitting this model to the 

data for each age group. The model fit depended upon the design of the experiment that 

generated the data. Two designs should be handled separately: experiments in which animals are 

exposed either as juveniles or as adults (with either a single or multiple dose in each period), and 

experiments in which exposure begins either in the juvenile or in the adult period, but once 

begun, continues through life. 

For the first case, the model equations are: 

(1) ( )

( )( )

0 0

e

0 0

1 (1 e )

1 1 e

A A

A J

m

A

m

J

P P P

P P P λ

δ

δ

−

−

= + − −

= + − −

where: 

subscripts A and J refer to the adult and juvenile period, respectively, 

λ is the natural logarithm of the juvenile:adult cancer potency ratio, 

P0 is the fraction of control animals with the particular tumor type being modeled, 

Px is the fraction of animals exposed in age period x with the tumor, 

mA is the rate of accumulation of “hits” per unit of time for adults, i.e., the cancer 

potency, and 

δx is the duration or number of exposures during age period x. 

For a substantial number of data sets (acute exposures), δJ = δA = 1. We are interested in 

 9
determining λ, which is the logarithm of the estimated ratio of juvenile to adult cancer potencies, 

a measure of potential susceptibility for early-life exposure. 

For the second kind of design, the model equations should take into account that 

exposures that were initiated in the juvenile period continue through the adult period. The model 

equations for the fraction of animals exposed only as adults with tumors in this design are the 

same as in the first design, but the fraction of animals whose first exposure occurred in the 

juvenile period is:

( ) ( ) ( ) e

0 0 1 1 e m m A J A A A P P J P λ − − δ δ − δ = + + − (2) 

All symbols in (eq. 2) have the same interpretation as their counterparts in (eq. 1), but 

now δJ includes the duration of exposure during the juvenile period as well as the subsequent 

adult period. 

Parameters in these models were estimated using Bayesian methods (see, for example, 

Carlin and Louis, 2000), and all inferences about the ratios were based on the marginal posterior 

distribution of λ. Some of these analyses, including a more complete description of the 

procedures (including the potential effect of alternative Bayesian priors that have been 

examined) have been published (Barton et al., 2005). The data for estimating each ratio were in 

the form of numbers of animals tested and number affected for each of control, juvenile-exposed, 

and adult-exposed animals, and duration of exposure for each of the juvenile-exposed and adultexposed groups. A few data sets had separate control groups for the juvenile-exposed and adultexposed groups, and equations 1 and 2 were modified accordingly. The likelihood for the 

parameters in the model was the product of three (or four, if there were two control groups) 

binomial probabilities: for the number of animals with tumors in the control group(s), for the 

juvenile-exposed group, and for the adult-exposed group. The prior for P0 (the fraction of 

control animals with a particular tumor) was right triangular (right angle at the origin), based on 

the assumption that control incidences should be relatively low. (The base of the distribution is 

one, as P0 can not exceed one. As this is a probability distribution, the area of the triangle is one. 

Therefore, its height at the origin must be 2.) The effect of exposure in adults is quantified by 

the extra risk, Q, where the probability that an animal has a tumor is P0+(1 – P0)Q. So, from

equations 1, 1 e Q −mAδ A = − , Q was given a uniform prior on the interval (0,1), reflecting total 

ignorance about the extra risk of adult exposure. Finally, the prior for λ was Gaussian with mean 

0 (corresponding to a median or geometric mean ratio of one) and standard deviation 3. The 

prior for the log ratio of juvenile to adult cancer potency has some influence over the posterior 

estimates for the ratio of juvenile to adult potency. The magnitude of that influence depends on 

 10
the amount of support in the data for different values of the log ratio. The prior also effectively 

downweights extremely large or small values for the juvenile to adult potency ratio. Three priors 

for the standard deviation were evaluated (Barton et al., 2005, see Appendix), with the intent of 

finding the largest prior, i.e., one that would contain the least informative assumption for the 

prior. A standard deviation of 9 was tried, but some of the intervals would not converge. A 

standard deviation of 3 worked well, allowed ratio estimates to be derived, with all of the data of 

interest. An intermediate value of 6 was also examined to ascertain if a less informative prior 

could be used. While the intervals converged, a sensitivity analysis showed that this value for the 

standard deviation resulted in sufficient down-weighting of the ratios with limited information 

that these data would not influence the result. This was considered an unreasonable bias, so a 

standard deviation of 3 was used for the further analyses. A further discussion of these analyses 

can be found in Barton et al. (2005). 

The posterior distribution for the unknown parameters in these models is the product of 

the likelihood from the data and the priors (the “unnormalized” prior), divided by a 

normalization constant that is the integral of the unnormalized prior over the ranges of all the 

parameters. This normalization constant was computed using numerical integration, as were 

posterior means and variances and marginal posterior quantiles for the log-ratio λ. All numerical 

computations were carried out in the R statistical programming language (version 1.8.1; R 

Development Core Team, 2003). 

This method produced a posterior mean ratio of the early-life to adult cancer potency, 

which is an estimate of the potential susceptibility of early-life exposure to carcinogens. If the 

ratio was greater than one, this indicated that the experiment found that there was greater 

susceptibility from early-life exposure. If the ratio was less than one, this indicated that the 

experiment found that there was less susceptibility from early-life exposure. Summaries of the 

individual ratios from each of the dose groups from the different experiments for different 

groupings were also calculated (for example for all acute exposures of chemicals that are 

carcinogenic by a mutagenic mode of action). The summary ratios were constructed from the 

individual ratios within a group, by variance-weighting the means of each ratio. The individual, 

posterior means were weighted by using reciprocals of their posterior variance. This weighting 

procedure is commonly used because it gives greater weight to those studies for which the 

variances, i.e., the uncertainties, are smaller. Because the ratios were calculated as log ratios (see

eq. 1), exponentiating the resulting inverse-variance-weighted mean yielded inverse-varianceweighted geometric means of ratios. 

 11
2.4. IONIZING RADIATION 

A supporting role was assigned to the available human radiation data, where cancer 

incidence in adults who were children at the time of the atomic bomb (A-bomb) exposure was 

compared with cancer incidence in adults who were older at the time of exposure. Although there 

are recognized differences in toxicokinetics and toxicodynamics between radiation and chemical 

carcinogens with a mutagenic mode of action, the data on A-bomb survivors provide information 

for many different cancer sites in humans with a single exposure involving all ages. In addition 

to the richness of the data, a number of national and international committees of experts have 

analyzed and modeled these data to develop risk estimates for various specific applications. 

The report of the United Nations Scientific Committee on the Effects of Atomic 

Radiation (UNSCEAR, 2000, with Scientific Annexes) lists more than 80 studies, in addition to 

the reports of the Japanese A-bomb survivors, in which at least one type of cancer was measured 

in humans who were exposed either intentionally or accidentally to some form of ionizing 

radiation. However only the A-bomb survivor reports have relevant information on incidence of 

early-life exposures. One of the more recent papers cited in the UNSCEAR report, by Thompson 

et al. (1994), contains detailed data on the incidence of 21 different cancers in 37,270 exposed Abomb survivors (42,702 unexposed). Also, EPA has used data from the A-bomb survivors to 

develop age-specific relative risk coefficients using various methods for transporting the risk 

from the Japanese population to the U.S. population (U.S. EPA, 1994). It is beyond the scope of 

this effort to present all of the radiation data or a discussion of the various analyses and modeling 

efforts. Rather, information relevant to comparing cancer risks from juvenile versus adult 

exposure from UNSCEAR (2000) and U.S. EPA (1994; 1999) is presented as representative 

findings to determine whether the radiation data are similar qualitatively to the chemical 

findings. More detailed data on the A-bomb survivors can be found in Delongchamp et al. 

(1997) and Preston et al. (2000).

As previously noted, several studies have assessed radiation in animal studies (Covelli et 

al., 1984; Di et al., 1990; Sasaki et al., 1978). However, lack of uniformity regarding radiation 

doses, gestational age at exposure, and the animal strains used make it difficult to compare the 

experimental data on cancer induction after prenatal irradiation (Preston et al., 2000). 

 12
3. RESULTS 

3.1. QUALITATIVE EVALUATION OF THE DATABASE 

The question addressed in this analysis was whether, and how, available quantitative 

scientific data could inform risk assessment policy choices for adjusting cancer slope factors 

when they are used in the assessment of cancer risk from childhood exposure. Cancer slope 

factors are, with few exceptions, based on adult human epidemiology or standard chronic adult 

rodent bioassays, which do not address the impacts of early-life exposures. Thus, the critical 

data are either human epidemiological data on childhood exposures resulting in adult cancer or 

research studies with rodents involving early postnatal exposures. The major human data 

available are from radiation exposures (studies summarized in Tables 9-11), with very limited 

data available for humans exposed during childhood to chemicals (reviewed in Anderson et al., 

2000; Miller et al., 2002). 

A review of the literature identified several hundred references reporting more than 50 

chemicals that have been shown to be able to cause cancer following perinatal exposure (Table 

1a) (reviewed in Toth, 1968; Della Porta and Terracini, 1969; Druckery, 1973, Rice, 1979; 

Vesselinovitch et al., 1979; Rice and Ward, 1982; Vesselovitch et al.; 1983; Fujii, 1991; 

Anderson et al., 2000). Studies (or groups of studies from a single laboratory on a given 

chemical) that directly provided quantitative data on carcinogenesis following early postnatal 

exposures and adult exposures to chemicals in animals were identified for 18 chemicals, listed in 

Table 1b, 2, and 3. Of the identified studies, there were 11 chemicals involving repeated 

exposures during early postnatal and adult lifestages (Table 1b) and 8 chemicals using acute 

exposures (typically single doses) at different ages (Table 1b). Some of the studies evaluated 

single tissues or organs for tumors (e.g., only liver), while others evaluated multiple tissues and 

organs (Tables 2 and 3). Mice, rats, or both species and sometimes multiple strains were tested. 

These studies serve as the basis for the quantitative analyses presented later in the results. 

In addition to the studies identified in Table 1b, studies were identified with early 

postnatal and early-life exposures that were evaluated qualitatively but not quantitatively. Some

of these studies are notable and provide important supporting information. Two recent studies 

used transgenic mouse models for human tumors. Increased multiplicity of colon tumors was 

observed following earlier versus later azoxymethane exposures (Paulsen et al., 2003). 

Shortened mammary tumor latency following estradiol exposure occurred when exposures 

occurred between 8 and 18 weeks as opposed to earlier or later, which is generally consistent 

with the incidence results analyzed for DMBA (Yang et al., 2003). Several notable examples 

exist of developmental windows leading to cancer susceptibilities that were not observable in 

 13
adults. Several potent estrogenic chemicals including DES, tamoxifen, and genistein produce 

uterine tumors with early postnatal exposures of mice, though there also appear to be straindependent differences in the tumor sites in adult mice (Gass et al., 1964; Greenman et al., 1990; 

Newbold et al., 1990, 1997, 1998, 2001). Developmental susceptibilities are believed to play a 

key role in effects observed with saccharin (Cohen et al., 1995; Whysner and Williams, 1996) 

and ascorbate (Cohen et al., 1998; NTP, 1983), with bladder tumors arising when early-life 

exposures occurred. Studies with several species, including rat, mouse, and opossum, indicate 

that nervous systems tumors associated with exposures to ENU and several other chemicals 

appear to be highly dependent upon exposures occurring within certain windows, particularly 

prenatal ones (Rice, 1979; Rice and Ward, 1982; Jurgelski et al., 1979). 

Analyses of the difference in cancer risk from exposures during different lifetime periods 

ideally should address both the period of potential susceptibility and the magnitude of the 

susceptibility. Available studies used a variety of study designs (see Tables 2 and 3), which can 

be valuable because they provide different information (Figure 1). However, variations in study 

design can result in a lack of comparability across chemicals, and can limit information on the 

consistency of effects with different chemicals acting through different modes of action. The 

acute dosing (largely single dose) studies (Table 3) are valuable because they involve identical 

exposures with explicitly defined doses and time periods demonstrating that differential tumor 

incidences arise exclusively from age-dependent susceptibility. These studies address both the 

period and magnitude of susceptibility. They were not as appropriate for quantitative 

adjustments for the cancer potency estimates because of their limitations, including that most 

used subcutaneous or ip injection that historically have not been considered quantitatively 

relevant routes of environmental exposure for human cancer risk assessment by EPA, and that 

these routes of exposure are expected to have only partial or a complete absence of first pass 

metabolism that is likely to affect potency estimates. 

The repeated dosing studies with exposures during early postnatal or adult lifetime 

provide useful information on the relative impact of repeated exposures at different lifestages 

and may be more likely to have exposure occur during a window of susceptibility, if there is one. 

One notable difference in study designs was that studies with repeated early postnatal exposure 

were included in the analysis even if they also involved earlier maternal and/or prenatal 

exposure, while studies addressing only prenatal exposure were not otherwise a part of this 

analysis. Another notable difference among studies involved the tissues that were evaluated for 

tumors: some studies focused on a single tissue, particularly liver, while others evaluated 

multiple tissues. 

Comparisons within a single repeated dosing study may have limitations for evaluating 

 14
differential susceptibility because exposures to the chemical can differ during the different 

lifestages, particularly when dietary or drinking water exposures are involved. A notable 

example is the PCB study (Chhabra et al., 1993a), in which mobilization of such lipid-soluble 

chemicals into mother’s milk would be expected to result in infants receiving much larger 

exposures than other lifestages. While lactational transfer is just as relevant to human nursing 

offspring, this difference in exposure obscures the extent to which the early lifestage is 

quantitatively more susceptible (i.e., part of the increased early-life cancer risk arises from higher 

exposure than during the adult period). Maternal metabolism of compounds such as 

diphenylhydantoin (DPH) (Chhabra et al., 1993b) also may result in lower exposure during 

lactation, potentially underestimating the early-lifestage risk, if the parent compound is the active 

form of the chemical. Similar issues exist due to normal age-dependent changes in food and 

water consumption. Ascribing differential effects observed in animal studies solely to lifestage 

susceptibility must be done carefully as there may also be differences in the exposures. There 

are substantial and clear benefits, therefore, from experimental consistency when comparisons 

are made directly within a study (e.g., same species and strain, consistent pathological 

evaluation). 

One issue to note is the rationale for the organization of the available data. It was 

observed that the results across a broad range of chemicals with a variety of modes of action 

were somewhat variable. Therefore, consistent with the approach of the EPA cancer guidelines 

(U.S. EPA, 2005), an approach based on mode of action appeared to be a common framework 

for analysis. Variability in lifestage-dependent susceptibility and susceptibility across a range of 

modes of action was further supported by theoretical analyses using multistage and two-stage 

models of carcinogenesis (Goddard and Krewski, 1995; Murdoch et al., 1992). 

3.2. QUANTITATIVE EVALUATION OF THE DATABASE 

As described in the Section 2.3, the potential difference in susceptibility between earlylife and adult exposure was calculated as the estimated ratio of cancer potency from early-life 

exposure over the cancer potency from adult exposure. Tables 4-7 present the results of the 

quantitative analysis using the studies that were determined qualitatively to have appropriate 

study designs (Tables 2 and 3) containing sufficient information to analyze. Based on the studies 

available, the calculations were organized into four tables: (1) compounds acting through a 

primarily mutagenic mode of action, where the compound was administered by a chronic dosing 

regimen to adults and repeated dosing in the early postnatal period (Table 4); (2) compounds 

acting through a primarily nonmutagenic mode of action, where the compound was administered 

by a chronic dosing regimen to adults and repeated dosing in the early postnatal period (Table 5); 

 15
(3) compounds acting through a primarily mutagenic mode of action, where the compounds were 

administered by an acute dosing regimen (Table 6); and (4) compounds acting primarily through 

either a mutagenic or nonmutagenic mode of action with chronic adult dosing and repeated early 

postnatal dosing (Table 7). In these tables, the 2.5% and 97.5% are percentiles of the posterior 

distribution. For a Bayesian distribution, these percentiles function in a manner similar to the 

95% confidence limits for other types of statistical analyses. The results are discussed below, 

followed by a description of results from analyses of studies of humans exposed to radiation. 

3.2.1. Carcinogens with a Mutagenic Mode of Action 

The most informative database on early-lifestage susceptibility exists for chemicals with 

a well-accepted mutagenic mode of action (e.g., diethylnitrosamine, vinyl chloride). This 

database includes both single-dose studies and repeated-dose studies involving periods of 

postnatal and/or chronic exposure. These studies help define the periods of increased 

vulnerability and the magnitude of the susceptibility. The acute dosing studies demonstrate that 

the age-dependent responses are not due to differences in exposure, because these studies 

explicitly control the exposure. 

3.2.1.1. Early Postnatal, Juvenile, and Adult Repeated Dosing Studies of Chemicals with a 

 Mutagenic Mode of Action 

Studies comparing repeated dosing for early-life, adult, or lifetime exposures exist for six 

carcinogens with a mutagenic mode of action [benzidine, diethylnitrosamine (DEN), 3-

methylcholanthrene, safrole, urethane, and vinyl chloride]; DEN also had acute dosing studies. 

Lifetime (i.e., combined juvenile and adult) compared to adult exposure studies were analyzed 

for DEN, safrole, and urethane, while studies comparing juvenile with adult exposures were 

analyzed for benzidine, 3-methylcholanthrene, safrole, and vinyl chloride. These chemicals all 

require metabolic activation to the active carcinogenic form. Analysis of the tumors arising per 

unit time of exposure found that juvenile exposures with each chemical could be more effective 

than adult exposures were at inducing tumors (Tables 4 and 7; Figure 2, a graphic representation 

of the posterior, unweighted geometric means and their 95% confidence intervals, for the ratios 

of juvenile to adult cancer potency for carcinogens acting through a mutagenic mode of action). 

The weighted geometric mean for repeat and lifetime exposures is 10.4; for acute exposures the 

weighted geometric mean value is 1.5. For benzidine and safrole, there was a notable sex 

difference, with high liver tumor incidence observed for early postnatal exposures of male, but 

not female, mice. For both the acute and the repeated/lifetime data, the 95th percentile of the 

individual, unweighted geometric means is above 10 (Figure 2). 

 16
This analysis focused upon the duration of exposure as a surrogate for dose, essentially 

assuming that the doses animals received during the different periods of these studies were 

similar. This assumption is a limitation of the analysis because these studies involved exposures 

via lactation (i.e., dosing the mother prior to weaning), drinking water, diet, or inhalation, which 

have the potential to deliver different doses at different lifestages. However, the range of the 

magnitudes of the tumor incidence ratios of juvenile to adult exposures is similar (Table 8) for 

the repeated dosing studies (0.12 – 111, weighted geometric mean 10.5, 42% of ratios greater 

than 1), lifetime dosing studies (0.18 – 79, weighted geometric mean 8.7, 67% of ratios greater 

than 1), and acute dosing studies (0.01 – 178, weighted geometric mean 1.5, 55% of ratios 

greater than 1), suggesting that these differences in dosing are not the sole determinant of the 

increased incidence of early tumors, i.e., uncertainty and variability remain. Because these 

comparisons include different chemicals with different tissue specificities, it may be informative 

to consider liver as a target organ affected by all of these chemicals. The range of the 

magnitudes of the liver tumor incidence ratios of juvenile to adult exposures is similar for the 

repeated dosing studies (0.12 – 111, weighted geometric mean 41.8, 86% of ratios greater than 1, 

Table 4), lifetime dosing studies (0.47 – 79, weighted geometric mean 14.9, 80% of ratios greater 

than 1, Table 7), and acute dosing studies (0.1 – 40, weighted geometric mean 8.1, 77% of ratios 

greater than 1, Table 8). Thus, the repeated dose studies support the concept that early-lifestage 

exposure to carcinogenic chemicals with a mutagenic mode of action would lead to an increased 

tumor incidence compared with adult exposures of a similar duration and dose. 

3.2.1.2. Acute Dosing Studies of Chemicals with a Mutagenic Mode of Action

Acute dosing studies are available for eight carcinogens with a mutagenic mode of action 

that were administered to mice or rats [benzo[a]pyrene (BaP), dibenzanthracene (DBA), 

Diethylnitrosamine (DEN), dimethylbenzanthracene (DMBA), dimethylnitrosamine (DMN), 

ethylnitrosourea (ENU), methylnitrosourea (NMU), and urethane (also known as ethyl 

carbamate)] (Table 1b). Except for ENU and NMU, these compounds require metabolic 

activation to their active carcinogenic forms. These acute dosing studies generally compared a 

single exposure during the first few weeks of life with the identical or similar exposure in young 

adult animals (Tables 3 and 6). Many of these studies compared exposures during the 

preweaning period (i.e., approximately day 21 for rats and mice) with effects around week 6, 

which is approximately the age at which typical chronic bioassays begin dosing animals. These 

studies largely were by subcutaneous or ip injection, which historically have not been considered 

quantitatively relevant routes of environmental exposure for human cancer risk assessment by 

EPA. For purposes of comparing age-dependent susceptibilities to tumor development, these 

 17
data are highly relevant. The injection route typically alters the pharmacokinetic time courses of 

the parent compound and the metabolites compared with oral or other exposures due to altered 

kinetics of absorption and metabolism. However, for these compounds and the systemic organ 

effects observed, there are several pharmacokinetic reasons to believe that the age-dependent 

trends would be similar with other routes of exposure. These compounds are expected to be 

reasonably well absorbed orally, comparable with injection routes, and largely require metabolic 

activation, so partial or complete absence of first pass metabolism in the injection studies would 

be similar to or underestimate metabolic activation when compared with oral exposure. 

The early exposures often resulted in higher incidence of tumors than later exposures, 

with increased early susceptibilities up to 178-fold (unweighted ratios in Table 6 range from

0.011 to 178, with a weighted geometric mean of 1.5, and 55% of ratios greater than 1, Figure 2, 

Table 8). Examples of the general age-dependent decline in susceptibility of tumor response 

include BaP (liver tumors), DEN (liver tumors), ENU (liver and nervous system tumors), and 

urethane (liver and lung tumors). While generally the Day 1 and Day 15 time points were higher 

than later time points, in several cases similar tumor incidence was observed at both these early 

times (e.g., ENU-induced kidney tumors, Tables 6 and 8). 

While the degree of susceptibility generally declines during the early postnatal period 

through puberty into early adulthood, there are exceptions due perhaps to pubertal periods of 

tissue development (e.g., mammary tissues) or very early development of xenobiotic 

metabolizing enzymes. One such exception was the increased incidence of mammary tumors in 

5-8 week old rats given DMBA, compared with older or younger rats (Meranze et al., 1969; 

Russo et al., 1979). Meranze et al. (1969) reported 8% mammary tumors following a single dose 

of DMBA at less than two weeks, 56% if given once to animals between 5 and 8 weeks old, and 

15% when given once to 26 week old rats. Thus, a ratio of 7.1 is obtained when comparing 

susceptibilities of 5–8 week and 26-week-old rats (Table 6) compared to a ratio of 0.2 when 

comparing the exposure at 2 weeks versus 26 weeks. A similar effect was observed by Russo et 

al. (1979); see Table 3. This observation corresponds well with pubertal development of the 

mammary tissue, with ovarian function commencing between 3 and 4 weeks (after the < 2 week 

time point in the Meranze et al., 1969 study), and mammary ductal growth and branching 

occurring such that it is approximately two-thirds complete by week 5, consistent with the 5–8 

week susceptible period of Meranze et al. (Silberstein, 2001). While this differs from the general 

trend previously discussed, it indicates susceptibility later in the juvenile period rather than 

earlier. Another example of deviation from the general trend toward an age-dependent decline is 

DEN-induced lung tumors that were somewhat lower in incidence following exposure on day 1 

than observed for the day 15 or day 42 exposures (Vesselinovitch et al., 1975) (Tables 3 and 6). 

 18
There are substantial differences in the early-life susceptibility of different tissues observed in 

the acute studies (Table 8). It should be noted that the target tissues vary with chemical, so the 

number of chemicals for which data are available varies for each tissue. Several tissues have 

weighted geometric mean ratios of greater than 1 including kidney, leukemia, liver, lymph, 

mammary, nerve, reticular tissue, thymic lymphoma, and uterus/vagina. Some of these, such as 

the nerve and mammary tumors, appear to have a very specific window of susceptibility, as 

noted above, and the ratios were much higher if the exposure occurred during this window. 

Tissues with weighted mean ratios less than 1 include forestomach, harderian gland, ovaries, and 

thyroid. Lung has a weighted geometric mean of 1. Many of the studies produced very high 

lung tumor responses regardless of age, so the results are difficult to interpret, as illustrated by 

the dose-response data with urethane in Rogers (1951) in which the increased early susceptibility 

is only apparent when the dose is low. The large numbers of studies with high lung tumor 

responses at all ages contribute to the differences in the weighted geometric means for the acute 

and for the repeated dosing studies. 

Overall, the acute dosing studies support the concept that early-lifestage exposure to 

carcinogenic chemicals with a mutagenic mode of action would lead to an increased incidence of 

tumors compared with adult exposures of a similar dose and duration. These studies generally 

use the same dose and duration at all ages, and thus do not have the type of issues discussed for 

the repeated dosing studies. On the other hand, the acute dosing studies have limitations that 

were sufficient to decide that they should not be included in the quantitative adjustment of cancer 

potency. First, as mentioned in the previous paragraph, the large number of studies of lung 

tumors with almost 100% response observed at all doses and all ages would significantly bias the 

median ratio toward unity for a reason based on study design rather than biology. Second, 

cancer potency estimates are usually derived from chronic exposures. Therefore, any adjustment 

to those potencies should be, if possible, from similar exposures. Third, most exposures of 

concern to the Agency are from repeated or chronic exposures rather than acute exposures. 

Finally, many of the acute studies used ip exposures, which is not the usual route of exposure for 

environmental chemicals. Thus, the repeated and lifetime studies are more appropriate for the 

purpose of this analysis. 

3.2.2. Carcinogens With Modes of Action Other Than Mutagenicity 

Studies comparing tumors observed at the same sites following early postnatal and 

chronic adult exposures in a single protocol were available for six chemicals that do not act 

through a mutagenic mode of action [amitrole, dichlorodiphenyltrichloroethane (DDT), dieldrin, 

ethylene thiourea (ETU), diphenylhydantoin (DPH), polybrominated biphenyls (PBB)] (Table 5). 

 19
These chemicals cause tumors through several different, not necessarily well defined, modes of 

action. For example, thyroid hormone disruption by ETU causes thyroid tumors; some PBBs act 

through aryl hydrocarbon (Ah) receptors, while others are phenobarbital-like pleiotrophic 

inducers of liver enzymes and liver tumors. Three of these studies evaluated only mouse liver 

tumors (amitrole, DDT, dieldrin), while the other three evaluated a large number of tissues in 

both mice and rats (ETU, DPH, PBB). These studies generally included a combined perinatal 

and adult exposure as well as the separate perinatal or adult-only groups. It should be noted that 

no acute perinatal dosing studies of carcinogenesis were identified for these agents; such 

protocols are generally considered largely non-responsive for modes of action other than 

mutagenicity and potent estrogenicity (e.g., DES). 

 For five chemicals (amitrole, DDT, dieldrin, PBB and DPH), the same tumors were 

observed from early and/or adult exposures, though the studies for amitrole, DDT, and dieldrin 

only evaluates the animals for liver tumors. With ETU, no tumors in mice or rats were observed 

following perinatal exposure alone (except a small, not-statistically-significant increase in male 

rat thyroid tumors), while thyroid tumors were observed in adult rats and thyroid, liver, and 

pituitary tumors in adult mice. Analysis of the incidence of tumors per time of exposure shows 

early-lifestage susceptibilities. The range of the magnitudes of the tumor incidence ratios of

juvenile to adult exposures is similar for the repeated dosing studies (0.06–13.3, weighted 

geometric mean 2.2, 27% of ratios greater than 1, Tables 5 and 8) and lifetime dosing studies 

(0.15–36, weighted geometric mean 3.4, 21% of ratios greater than 1, Tables 7 and 8). These 

ranges and means are similar to those for chemicals with a mutagenic mode of action, though the 

means and maximums are somewhat lower. Again, liver tumors are common to these chemicals. 

The range of the magnitudes of liver tumor incidence ratios of juvenile to adult exposures also is 

similar for the repeated dosing studies (0.06–13.3, weighted geometric mean 2.6, 43% of ratios 

greater than 1, Tables 5 and 8) and lifetime dosing studies (0.15–36, weighted geometric mean 

5.8, 33% of ratios greater than 1, Tables 7 and 8).

The major factor that complicates the interpretation of the results is that these studies, 

except with DDT and dieldrin, involved dietary feeding initially to the mother, which potentially 

could increase or decrease the dose received by the pups. Due to the maternal dosing during 

pregnancy and lactation, the extent to which offspring received similar doses during different 

early and adult lifestages is particularly uncertain for DPH, ETU, and PBBs. Oral gavage doses 

in young animals were selected to approximate the average daily dose in adult dietary studies 

based on standard estimates of feed consumption in the studies with DDT and dieldrin, while the

amitrole study involved dietary feeding postnatally to the mother so the young were dosed via 

lactation. In addition, DDT, dieldrin, and some PBBs are more persistent in the body than are 

 20
most chemicals, leading to a prolonged exposure even following limited dosing. Thus, these 

studies provide evidence that early lifestages can be more susceptible to exposures to chemicals 

causing cancer through a variety of modes of action other than mutagenicity. However, the 

studies with ethylene thiourea, which acts via thyroid disruption, indicate that this is not 

necessarily the case for all modes of action. 

 

3.2.3. Ionizing Radiation 

As mentioned previously, the UNSCEAR, Annex I (2000) includes information derived 

from a wide range of both intentional (generally diagnostic or therapeutic medical) and 

accidental radiation exposures. Only information derived from the Japanese population (referred 

to as the Life Span Study in the UNSCEAR Annex I) is presented here. A statistically significant 

excess cancer mortality associated with radiation has been found among the bomb survivors for 

the following types of cancer: esophagus, stomach, colon, liver, lung, bone and connective 

tissue, skin, breast, urinary tract, and leukemia. Tables 9 and 10 are extracted from the tables in 

UNSCEAR, Annex I. The excess relative risk (ERR) is the increased cancer rate relative to an 

unexposed population; an ERR of 1 corresponds to a doubling of the cancer rate. Because of the 

low numbers of cancers in individual sites within narrow age groups, the ERRs for the various 

solid tumors and leukemia were presented only as less than or greater than 20 years of age at the 

time of exposure. The larger number of thyroid tumors enable a more detailed breakout shown in 

Table 10. Most sites show greater risks in the younger than in the older ages. 

The U.S. EPA (1994) document presents a methodology for estimation of cancer risks in 

the U.S. population due to low-LET (linear energy transfer) radiation exposures using data from

the Atomic Bomb Survivor Study (ABSS) as well as from selected medical exposures. The 

report developed mortality risk coefficients using several models that took into account age and 

gender dependence of dosimetry, radiogenic risk, and competing causes of death as well as 

transporting of risks across populations. The risk projections were updated using more recent 

vital statistics in a report that also included an uncertainty analysis (U.S. EPA, 1999). Details of 

the derivation of these coefficients are available at 

http://www.epa.gov/radiation/docs/rad_risk.pdf . 

Table 11 contains the calculated age-specific risk coefficients derived from the 

application of the various models to the ABSS data. For most of the sites in the table, the risk 

coefficients are higher in the earlier age groups; liver, bone, skin, and kidney coefficients are 

age-independent and only esophageal cancer coefficients increase with increasing age. Also of 

note is that the coefficients generally are higher for females. Similar to the information from the 

UNSCEAR (2000) Annex, most sites show greater risks in the younger ages than the older ages. 

 21
However, a comparison of the two tables seems to show reversal of risks for some sites as a 

function of age at exposure. While the high sampling variability in the epidemiological data for 

some ages may contribute to this apparent reversal, the choice of risk models and associated 

parameters also is a factor. 

 22
4. DISCUSSION 

The challenge for this analysis was how to use the existing, but limited, scientific 

database on early postnatal and juvenile exposures to carcinogens to inform a science policy 

decision on whether, and if so how, to assess the risk from childhood exposures to chemicals for 

which we have evidence of carcinogenicity only in adult humans or sexually mature laboratory 

animals. The database overall is of limited size (particularly compared with the number of 

chemicals that have been studied in adult occupational epidemiological studies or chronic 

bioassays). The majority of the human data involves exposures to ionizing radiation or DES 

(Anderson et al., 2000). More than 50 chemicals have been demonstrated to cause cancer 

following perinatal exposures in animals (without adult exposures), but only a subset of the 

chemicals have comparative studies across ages. The comparative experimental studies used 18 

chemicals, 12 of which had mutagenic modes of action and 6 of which had data from repeated or 

lifetime exposures. Other analyses of similar data have found similar results (Hattis et al. 2005), 

but have focused on other aspects of the data, e.g., gender differences. 

Previously published or internal U.S. EPA analyses have concluded that the standard 

animal bioassay protocols usually do not miss chemicals that would have been identified as 

carcinogens if perinatal exposures had been undertaken (McConnell, 1992; Miller et al., 2002; 

U.S. EPA, 1996). Given the increased complexity and costs of chronic bioassays with perinatal 

exposures, a limited number of such studies have been performed. However, these are the 

studies that largely constitute the available database for this analysis. In addition to the chronic 

bioassays with perinatal exposures, there are studies with acute dosing at different lifestages and 

a large number of studies with perinatal exposures without a directly comparative adult study. 

Two other kinds of information can contribute toward developing a scientifically 

informed policy: theoretical analyses and analyses of stop studies.4

 Theoretical analyses suggest 

that the differential susceptibility would depend in part on the mode of action (i.e., at what step 

in the cancer process(s) the chemical was acting) and that the use of the average daily exposure 

prorated over a lifetime may underestimate or overestimate the cancer risk when exposures are 

time-dependent (Goddard and Krewski, 1995; Murdoch et al., 1992). Evidence for oldage-dependent promotion of basophilic foci in rats by peroxisome proliferators appears to 

provide a concrete example consistent with these theoretical analyses (Cattley et al., 1991; 

Kraupp-Grasl et al., 1991). The stop studies performed by the National Toxicology Program

began exposure at the standard post-weaning age, but stopped exposure after varying periods of 

months. Other groups of animals were exposed for a full two years; all animals were evaluated 

 4

 Stop studies are studies in which exposure is halted after a predetermined period. 

 23
for tumors at the end of two years regardless of the duration of exposure (Halmes et al., 2000). 

Related data also are available from the stop studies with vinyl chloride (Drew et al., 1983). 

Analysis by Halmes et al. (2000) showed that, for six of the eleven chemicals and half the tumor 

sites, the assumption that the cancer risk would be equal when the product of concentration and 

time (i.e., C x T) was constant was incorrect, and usually underestimated risk, as more of the risk 

came from the beginning of the exposure rather than the end. This dependence of risk on both 

duration and intensity of exposure did not appear to be correlated with mutagenicity. It should 

be noted that these stop studies all involved exposures early in the life of the animal (as opposed 

to a limited number of cancer studies that looked at later periods of life; e.g., Drew et al., 1983), 

but the extent to which the differences in tumor outcome result from increased susceptibility in 

these early periods or the extended period for expression of the cancer cannot be evaluated. 

These stop studies also used doses as high as or higher than the highest dose used in the two-year 

exposure. This latter factor clearly had a significant effect for two chemicals, causing tumors at 

higher doses that were not observed at lower doses. These results suggest that pharmacokinetic 

or other dose-rate dependencies can make the effects of exposures at high doses different from

those exposures at lower doses. While not directly informative about early childhood exposures, 

these studies provide a perspective on the common cancer risk assessment practice of averaging 

exposures over a lifetime, especially those that include earlier lifestages. Thus, alternative 

methods for estimating risks from short-term exposures during childhood should be considered. 

Information on different lifestage susceptibilities to cancer risks for humans exists for 

ionizing radiation. The effects of chemical mutagens at different lifestages on cancer induction 

are derived from laboratory animal studies. While the induction of cancer by ionizing radiation 

and the induction of cancer by chemical mutagens are not identical processes, both involve direct 

damage to DNA as critical causal steps in the process. In both cases, the impacts of early 

exposure can be greater than the impacts of later exposures, probably due to some combination 

of early-lifestage susceptibility and the longer periods for observation of effects. As indicated in 

Tables 9 and 10, A-bomb survivors exhibited different lifestage dependencies at different tumor 

sites, though the total radiation-related incidence of tumors showed a general slow decline with 

age at exposure. However, as previously noted, there are apparent differences at some sites 

between the two tables. In addition to the sampling and modeling differences, the excess risk 

values in Table 9 are based on Japanese baselines while the coefficients in Table 10 reflect 

UNSCEAR’s effort to transport the risks from the Japanese population to that of the United 

States. However, it is clear that the total radiation-related tumor incidence showed a general slow 

decline with age at exposure. 

The studies in rodents of chemicals with mutagenic modes of action similarly support a 

 24
general decline in induced cancer risk with age at exposure and similarly show some differences 

for individual tumor sites. In general, the earliest two or three postnatal weeks in mice and rats 

appeared to be the most susceptible, though some degree of increased susceptibility through 

puberty in rats (beginning around 5–7 weeks) and mice (beginning around 4–6 weeks) for some

types of tumors exists. 

All the acute dosing studies that demonstrated carcinogenicity with animals of different 

ages used chemicals with a mutagenic mode of action (Tables 4 and 6). These studies provide 

the clearest demonstrations of periods of differential susceptibility because the exposure rate is 

constant at the different ages. The repeated dose studies also include several of the most 

informative studies for assessing perinatal carcinogenesis, notably those on vinyl chloride and 

DEN (Tables 2 and 4). The vinyl chloride studies by Maltoni and colleagues are part of a large 

series of studies on this compound that included exposures to different concentrations for 

varying durations, including some at early lifestages (Maltoni et al., 1984). The DEN study by 

Peto et al. (1984) used a unique chronic study design in which groups of rats were exposed to 

multiple drinking water concentrations starting at 3, 6, or 20 weeks of life. This design provides 

information on the susceptibility of early exposure periods within a nearly lifetime exposure. 

Beyond the analysis described here, there are conceptual biological rationales that would 

suggest DNA-damaging agents would have greater impacts on early lifestages. Growth involves 

substantial levels of cell replication, even in organs that in adults are only very slowly 

replicating, thus increasing the likelihood that a cell will undergo division before the DNA 

damage caused by the mutagen has been repaired. Increased replication also can lead to a 

greater division of initiated cells, leading to a larger number of initiated cells per specified dose. 

These periods of cell replication can vary for different tissues. For example, DMBA appears to 

be more effective at initiating mammary tumors in 6-8 week old rats, which are undergoing 

development of that tissue, than during earlier or later periods (Meranze et al., 1969). While 

tumor promotion processes can be very dependent upon the duration of promotion, initiation 

processes can occur in relatively brief periods (e.g., the single-dose studies in animals or 

radiation exposure in humans). Most tumors take extended periods to develop, making damage 

that occurs earlier in life more likely to result in tumors prior to death than would exposures that 

occur later in life. While some of these observations may also pertain to other modes, all of them

(with some differences among tumor sites) appear to be potentially relevant to a greater 

susceptibility to mutagenic modes of action during early-life stages (vs. later-life stages). 

The information on lifestage susceptibility for chemicals inducing cancers through modes 

of action other than direct DNA interaction is more varied, showing an increase in tumor 

incidence during perinatal exposure versus exposures of mature animals (e.g., polybrominated 

 25
biphenyls induced liver tumors), no tumors from perinatal exposure (e.g., ethylene thiourea 

induced thyroid tumors), no effect of combined perinatal and adult exposure (e.g., DPH liver 

tumors in rats and female mice), and different tumors from perinatal exposure versus adult 

exposure (e.g., DES, ascorbate). These variations are likely a result of the modes of action of 

these chemicals and the pharmacokinetic differences in doses during different periods of life. No 

studies were evaluated that were directly comparable to the single-dose studies with mutagens, 

which clearly show significant differences in tumor responses after explicitly controlled doses at 

different lifestages. 

Some evidence for an effect of early-lifestage exposures on tumor incidence was 

observed in studies with polybrominated biphenyls, amitrole, DDT, dieldrin, and 

diphenylhydantoin. These studies show increased incidence of tumors in mice from perinatal 

exposure, though only those for polybrominated biphenyls were statistically significant. (A 

nonstatistically significant increase also was observed in male rats with polybrominated 

biphenyls.) Combined perinatal and adult exposures generally gave statistically significant 

increases, though not necessarily for each sex and species (rat and mice) in the 

diphenylhydantoin and polybrominated biphenyl studies. 

There are important demonstrations of chemicals acting through modes of action other 

than mutagenic to cause different tumor types with early-lifestage exposures compared with 

exposures for adults, e.g., tamoxifen and DES (Carthew et al., 2000; Carthew et al., 1996, Gass 

et al., 1964; Newbold et al., 1990, 1997, 1998). In addition, studies with in utero exposure to 

atrazine (Fenton and Davis, 2002), DES, and arsenic (Waalkes et al., 2003) indicate that earlylife exposures to compounds can alter susceptibility of endocrine and reproductive organs. Three 

of these compounds (i.e., DES, genistein, and tamoxifen) bind to the estrogen receptor. Ongoing 

studies on ethinyl estradiol, nonylphenol, and genistein by the National Toxicology Program will 

add to this database for estrogens (Laurenzana et al., 2002; Newbold et al., 2001). These studies 

will evaluate cancer incidence in offspring exposed in utero, during lactation, and through 

adulthood via diet. A study with genistein found uterine tumor development to be dependent 

upon early-lifestage exposures (Newbold et al., 2001). Another recent study of estrogen found a 

shorter latency for mammary tumors in mice exposed at 8 and 12 weeks as compared to mice 

exposed at 4 or 18 weeks, indicating a susceptible period between 8 to 12 weeks of exposure 

(Yang, 2003). Thus, there is an actively growing database from which to consider issues of 

childhood exposure and cancer for compounds acting through the estrogen receptor or other 

mechanisms of endocrine disruption. 

The ability to estimate with any accuracy the juvenile to adult cancer potency ratio 

depends very much on the experimental design used. The lifetime design has less ability to 

 26
distinguish increased susceptibility from early-life exposure than the other types of designs. 

Consider two different experimental designs. In the first, the “lifetime” design, a group of 

animals are exposed starting as juveniles, and exposure continues through adulthood. A second 

group are exposed only in adulthood, and the juvenile:adult ratio results from a comparison of 

tumor incidences in the two groups. In the second, the “repeated” design, one group of animals 

is exposed only during the juvenile period, and is then followed through adulthood to assess 

tumor incidence, and a second group of animals is exposed only through adulthood. The lifetime 

design turns out to be a particularly insensitive design for estimating the juvenile:adult ratio. 

The following example demonstrates the magnitude of the problem: Suppose the risk per 

day of exposure of a chemical is ten fold greater in the juvenile period as in the adult period, and 

animals exposed through adulthood at a particular dose level have an extra risk of 60% for 

having at least one tumor, while 1% of control animals have tumors. The adult exposure period 

is 94 weeks, while the juvenile exposure period is 4 weeks. Thus, in the lifetime design, the 

group of animals exposed as juveniles will receive a total of 98 weeks of exposure, (4 in juvenile 

and 94 in adult), while those receiving the adult-only exposure receive 94 weeks of exposure. In 

the repeated design, animals exposed as juveniles receive only 4 weeks of exposure, while the 

adults receive 94 weeks, just as in the lifetime design. Each group starts with 50 animals. Under 

these assumptions, using equations (1) and (2) from Section 2.3, the expected number of animals 

with tumors in the three treatment groups (control, juvenile-exposed, adult-exposed groups) in 

the two designs is: 

Number of animals with tumors

Control Early-life exposure Adult exposure

Lifetime 1 36 30

Repeated 1 16 30

Notice that in the “lifetime” design, only six more juvenile-exposed animals have tumors 

than in the adult-exposed group, whereas in the “repeated” design, 16 juvenile-exposed animals 

have tumors. The data in the lifetime design are consistent with the hypothesis of no tumors 

being induced during the juvenile period: the ratios 36/50 and 30/50 are not statistically 

significantly different. In other words, the data from the lifetime design are statistically 

consistent with the hypothesis of no risk at all during the juvenile period, even though the real 

response is a 10 times greater risk from early-life exposure. The difference between the results 

from the two different study designs is due to the one-hit model: each additional week of a long 

exposure contributes less than the previous week to the total number of animals with tumors. 

 27
Note that, even if the one-hit model is not correct, chronic exposure probably results in a nonstatistically significant increase for the lifetime exposure including juveniles as compared with 

only adult exposure. 

The proper measure of relative potency of an exposure in the juvenile period relative to 

an exposure in the adult period is the ratio of doses in the two periods that give the same

incidence of tumors. However, most of the data sets used in this report contained only one noncontrol dose, precluding the extensive dose-response modeling that would be required to 

estimate this ratio of doses. However, this document largely considered chemicals for which a 

mutagenic mode of action has been established and for which a linear, no-threshold doseresponse function is assumed for the low-dose range being considered for risk assessment. In the 

case of the linear dose-response function, the analysis of the relative response from the same

dose will produce the same value as ratio of doses that produces the same incidence of tumors. 

For a one-hit dose-response equation, the probability of developing a tumor after the 

same dose and duration in the juvenile or adult period is 

( )

( ) m x

j

m x

a

j

a

P P e

P P e

−

−

= − −

= − −

0

0

1 1

1 1

for dose x. Suppose we want to calculate the dose Da or Dj that results in a given incidence of 

tumors after an adult or juvenile exposure. From equation 1, Da and Dj equal: 

j

c

j

a

c

a

m

P

P

D

m

P

P

D

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

− −

=

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

− −

=

0

0

1

1 ln

1

1 ln

Thus, the ratio Da/Dj = mj/ma, the ratio calculated in this document. 

In summary, this analysis supports the conclusion that there can be greater susceptibility 

for the development of tumors as a result of exposures to chemicals acting through a mutagenic 

mode of action, when the exposures occur in early lifestages as compared with later lifestages. 

Thus, this Supplemental Guidance recommends for chemicals with a mutagenic mode of action 

for carcinogenesis when chemical-specific data on early-life exposure are absent, a default 

 28
approach using estimates from chronic studies (i.e., cancer slope factors) with appropriate 

modifications to address the potential for differential risk of early-lifestage exposure. For 

chemicals acting through a non-mutagenic mode of action, e.g., hormonally mediated 

carcinogens, the available data suggest that other approaches may need to be developed for 

addressing cancer risk estimates from childhood exposures. This is a particular concern because 

the tumors arising from hormonally active chemicals appear to involve different sites when 

exposure is during early-life versus adulthood, an effect that has been observed relatively 

infrequently. Development of such approaches would require additional research to provide an 

expanded scientific basis for their support, including additional research and the possible 

development of new toxicity testing protocols that consider early lifestage dosing. 

The current data do also not allow analysis of some issues of potential interest for risk

assessment, e.g., potential increased risk of childhood cancer, from in utero or childhood 

exposures. Assessing the role of environmental exposures on childhood cancers is difficult, but 

additional research could include epidemiological studies or experimental studies with animals 

genetically designed to express cancers analogous to human childhood cancers. Rigorous 

quantification of exposure doses at different lifestages and in rodent pups in experimental studies 

would be useful for evaluating whether there is greater childhood susceptibility. 

Pharmacokinetic modeling could better define the internal doses to improve determination of the 

magnitude of increased susceptibility.

 29
5. GUIDANCE FOR ASSESSING CANCER RISKS 

FROM EARLY-LIFE EXPOSURE 

Consistent with the approach and recommendations of the U.S. EPA cancer risk 

assessment guidelines (U.S. EPA, 2004), any assessment of cancer susceptibility will begin with 

a critical analysis of the available information. Figure 3 shows the proposed steps in the process. 

The potential for increased susceptibility to cancer from early-life exposure, relative to 

comparable exposure later in life, generally warrants explicit consideration for each assessment. 

When developing quantitative estimates of cancer risk, the Agency recommends 

integration of age-specific values for both exposure and toxicity/potency where such data are 

available and appropriate. Children, in general, are expected to have some exposures that differ 

from those of adults (either higher or lower), due to differences in size, physiology, and 

behavior. For example, children are generally assumed to eat more food and drink more water 

relative to their body weight than adults. Children’s normal activities, such as putting their hands 

into their mouths or playing on the ground, can result in exposures to contaminants that adults do 

not encounter. Moreover, children and adults exposed to the same concentration of an agent in 

food, water, or air may receive different (higher or lower) internal doses due to differences, for 

example, in intake, metabolism, or absorption rates. Children are less likely than adults to be 

exposed to products typically used in industrial settings and often have more limited diets than 

adults. When assessing risks, if the data are available and relevant, it is important to include 

exposure that is measured or modeled for all lifestages, including exposures during childhood 

and during adulthood. EPA continues to develop better tools for assessing childhood exposure 

differences, such as the Child-Specific Exposure Factors Handbook (U.S. EPA, 2002a), and 

models, such as Stochastic Human Exposure and Dose Simulation (SHEDS) and Consolidated 

Human Activity Database (CHAD) (McCurdy et al., 2000; Zartarian et al., 2000) 

Mode-of-action studies can be a source of data on quantitative differences between 

children and adults (Figure 3, Box 1). If the available information is sufficient to establish the 

agent’s mode of action for early-life and adult exposures, then the implications for early-life 

exposure of that mode of action are used to develop separate risk estimates for childhood 

exposure. Pertinent information can be obtained both from agent-specific studies and from other 

 30
studies that investigate the general properties of the particular mode of action. All data 

indicating quantitative differences between children and adults are considered in developing 

those portion(s) of the risk estimates for exposure estimates that include childhood exposure. 

Some examples include the potential for children to have a different internal dose of the active 

agent or a change in a key precursor event (see Section 2.4.3.4 of the Guidelines for Cancer Risk

Assessment). 

When the mode of action cannot be established (Figure 3, Box 2), the policy choice 

would be to use linear extrapolation to lower doses such that risk estimates are based on a 

lifetime average daily exposure without further adjustment. No general adjustment is 

recommended at this time. This policy choice is consistent with past U.S. EPA practice that has 

been favorably evaluated over the years. The result would be expected to produce plausible 

upper bound risk estimates, based on the use of linear extrapolation as a default in the absence of 

information on the likely shape of the dose-response curve. 

When a mode of action other than mutagenicity is established, if it is nonlinear (Figure 3, 

Box 3) or linear (Figure 3, Box 4), no general adjustment is recommended at this time. Although 

the available studies (discussed previously) indicates that higher or lower cancer risks may result 

from early-life exposure, there is insufficient information or analyses currently available to 

determine a general adjustment at this time. As other modes of action become better understood, 

this information may include data on quantitative differences between children and adults. If 

such data are available, an analysis of the differences could be used to adjust risk estimates for 

childhood exposure. EPA expects to expand this Supplemental Guidance to specifically address 

modes of action other than mutagenicity when sufficient data are available and analyzed. 

When the data indicate a mutagenic mode of action,5

 the available studies (discussed 

 

5 Determination of chemicals that are operating by a mutagenic mode of action entails evaluation of test results for

genetic endpoints, metabolic profiles, physicochemical properties, and structure-activity analyses in a weight-ofevidence approach (Waters et al., 1999). Established protocols are used to generate the data (Cimino, 2001; OECD, 

1998; U.S. EPA, 2002b); however, it is recognized that newer methods and technologies such as those arising from

genomics can provide useful data and insights to a mutagenic mode of action. Carcinogens acting through a 

mutagenic mode of action generally interact with DNA and can produce such effects as DNA adducts and/or 

breakage. Carcinogens with a mutagenic mode of action often produce positive effects in multiple test systems for 

different genetic endpoints, particularly gene mutations and structural chromosome aberrations, and in tests 

performed in vivo, which generally are supported by those performed in vitro. This mode of action is addressed in

more detail in Section 2.3.5 of EPA’s cancer guidelines (U.S. EPA, 2005). 

 31
above) indicate higher cancer risks resulting from a given exposure occurring early in life when 

compared with the same amount of exposure during adulthood. However, chemical-specific data 

relating to mode of action (e.g., toxicokinetic or toxicodynamic information) may suggest that 

even though a compound has a mutagenic mode of action, higher cancer risks may not result. 

Such data should be considered before applying the age-dependent adjustment factors. 

If the available, chemical-specific information includes an epidemiologic study of the 

effects of childhood exposure or an animal bioassay involving early-life exposure (Figure 3, Box 

5), then these studies are analyzed to develop risk estimates (i.e., cancer slope factors) that 

specifically address any potential for differential potency in early lifestages. An example is the 

IRIS assessment of vinyl chloride (U.S. EPA, 2000b; c). 

In the absence of early-life studies on a specific chemical under consideration (Figure 3, 

Box 6), the extrapolation from the point of departure to lower doses employs linear extrapolation 

(see Section 3.3.1 of the U.S. EPA [2005] cancer guidelines). This choice is based on mode-ofaction data indicating that mutagens can give rise to cancers with an apparently low-dose linear 

response. Adjustments to the resultant risk estimates are specified with regard to childhood 

exposures. This approach is adopted because risk estimates based on an average daily exposure 

prorated over a lifetime do not consider the potential for higher cancer risks from early-life 

exposure. 

The adjustments described below reflect the potential for early-life exposure to make a 

greater contribution to cancers appearing later in life. The 10-fold adjustment represents an 

approximation of the weighted geometric mean tumor incidence ratio from juvenile or adult 

exposures in the repeated dosing studies (see Table 8). This adjustment is applied for the first 2 

years of life, when toxicokinetic and toxicodynamic differences between children and adults are 

greatest (Ginsberg et al., 2002; Renwick, 1998). Toxicokinetic differences from adults, which 

are greatest at birth, resolve by approximately 6 months to 1 year, while higher growth rates 

extend for longer periods. The 3-fold adjustment represents an intermediate level of adjustment 

that is applied after 2 years of age through <16 years of age. This upper age limit represents 

middle adolescence following the period of rapid developmental changes in puberty and the 

conclusion of growth in body height in NHANES data (Hattis et al., 2005). Efforts to map the 

approximate start of mouse and rat bioassays (i.e., 60 days) to equivalent ages in humans ranged 

from 10.6 to 15.1 years (Hattis et al., 2005). Data are not available to calculate a specific doseresponse adjustment factor for the 2 to <16-year age range, so EPA selected the 3-fold 

 32
adjustment because it reflects a midpoint, i.e., approximately half the difference between 1 and 

10 on a logarithmic scale (101/2), between the 10-fold adjustment for the first two years of life 

and no adjustment (i.e., 1-fold) for adult exposure. EPA also recognizes that exposures 

occurring near the end of life may have little effect on lifetime cancer risk, but lacks adequate 

data at present to provide an adjustment for this "wasted dose" effect. Similarly, since most of 

the studies involved only one latency period, the potential effect of early-life exposure on latency 

for the observed tumors could not be evaluated. The lack of data on effect on latency also 

limited the types of analyses that could be performed, e.g., more complex dose-response 

functions, such as multi-stage or clonal expansion models, could not be evaluated. Thus, the 

potential effects of early-life exposures on latency were not evaluated. Finally, as the adjustment 

factors are derived from a weighted geometric mean of the data evaluated, these adjustment will 

both over-estimate and under-estimate the potential potency for early-life exposure for chemicals 

with a mutagenic mode of action for carcinogenesis. An examination of the data in the tables 

demonstrates that some of the ratios were less than one, while others exceeded 10. For this 

reason, the Supplemental Guidance emphasizes that chemical-specific data should be used in 

preference to these default adjustment factors whenever such data are available. 

The following adjustments represent a practical approach that reflects the results of the 

preceding analysis, which concluded that cancer risks generally are higher from early-life 

exposure than from similar exposure durations later in life: 

• For exposures before 2 years of age (i.e., spanning a 2-year time interval from the first 

day of birth up until a child’s second birthday), a 10-fold adjustment. 

• For exposures between 2 and <16 years of age (i.e., spanning a 14-year time interval from

a child’s second birthday up until their sixteenth birthday), a 3-fold adjustment. 

• For exposures after turning 16 years of age, no adjustment. 

Clearly other age groups, such as an age group experiencing pubertal changes in 

physiology, or approximately ages 9 - 15, may experience changes in biological processes that 

could lead to modifications in the susceptibility to the effects of some carcinogens, depending on 

the mode of action. This Supplemental Guidance focuses on carcinogens with a mutagenic mode 

 33
of action. For any mode of action, the Agency is interested in identifying lifestages that may be 

particularly sensitive or refractory for carcinogenesis, and believes that the mode of action 

framework as described by EPA’s cancer guidelines (U.S. EPA, 2005), is an appropriate 

mechanism for elucidating these lifestages. In general, the Agency’s analyses of lifestages that 

may be susceptible will depend on three factors: (1) establishing the mode of action for 

carcinogenesis; (2) using knowledge about the biological and toxicological key events in that 

mode of action that are likely to be affected by lifestages; and (3) the availability, or 

development, of data that allow analysis of the effects of chemicals acting by that mode of action 

during the relevant ages. For each mode of action evaluated, therefore, the various age groupings 

determined to be at a differential risk, which may differ significantly from those proposed for the 

mutagenic mode of action, are expected to be evaluated independently of other modes of action. 

When data, including well established mode of action data, are available that allow specific 

evaluation of lifestage differences in toxicokinetics or toxicodynamics that would lead to lesser 

or greater susceptibility from early-life exposures to carcinogens, then those data should be used, 

as generally discussed in EPA’s cancer guidelines (U.S. EPA, 2005), in preference to the default 

procedures described in this Supplemental Guidance. 

The 10-fold and 3-fold adjustments in slope factor are to be combined with age-specific 

exposure estimates when estimating cancer risks from early life exposure to carcinogens that act 

through a mutagenic mode of action. It is important to emphasize that these adjustments are 

combined with corresponding age-specific estimates of exposure to assess cancer risk. For 

example, for a 70-year lifetime, where there are data showing negligible exposure to children, 

the estimated cancer risk from childhood exposure would be also negligible and the lifetime 

cancer risk would be reduced to that resulting from the relevant number of years of adult 

exposure (in the absence of specific information, 55 years). Where there are data (measured or 

modeled) for childhood exposures, the age-group specific exposure values are used along with 

the corresponding adjustments to the slope factor. Where there are no relevant data or models 

for childhood exposures and only lifetime average exposure data are available, the lifetime 

exposure data are used with the adjustments to the slope factor for each age segment. 

It is recognized that, when the exposure is fairly uniform over a lifetime, the effect of 

these adjustments on estimated lifetime cancer risk are small relative to the overall uncertainty of

 34
such estimates. These adjustments can be applied when estimating the cancer risk resulting from

childhood exposure. These adjustments are applied when developing risk estimates from

conventional animal bioassays or epidemiologic studies of effects of adult exposure. Some

examples follow in the next section. 

The Agency has also carefully considered both the advantages and disadvantages to 

extending the default potency adjustment factors to carcinogenic chemicals for which the mode 

of action remains unknown. It is the Agency’s long-standing science policy position that use of 

the linear low-dose extrapolation approach (without further adjustment) provides adequate public 

health conservatism in the absence of chemical-specific data indicating differential early-life 

susceptibility. At the present time, therefore, EPA is recommending these age-dependent 

adjustment factors only for carcinogens acting through a mutagenic mode of action based on a 

combination of analysis of available data and the above-mentioned science policy position. In 

general, the Agency prefers to rely on analyses of data, rather than general defaults. When data 

are available for a susceptible lifestage, they should be used directly to evaluate risks for that 

chemical and that lifestage on a case-by-case basis. In this analysis, the data for non-mutagenic 

carcinogens, when the mode of action is unknown, were judged to be too limited and the modes 

of action too diverse to use this as a category for which a general default adjustment factor 

approach can be applied. 

 35
6 COMBINING LIFESTAGE DIFFERENCES IN EXPOSURE AND DOSERESPONSE WHEN ASSESSING CARCINOGEN RISK - SOME EXAMPLES FOR 

CARCINOGENS THAT ACT THROUGH A MUTAGENIC MODE OF ACTION 

It is important for the risk assessor to consider lifestage differences in both exposure and 

dose-response when assessing cancer risk resulting from early-life exposures. As discussed in 

Section 5, age dependent adjustments factors (ADAFs) in dose response (i.e., slope factors) are 

combined with age specific exposure estimates when assessing cancer risks. This is a departure 

from the way cancer risks have historically been based upon the premise that risk is proportional 

to the daily average of lifetime dose. This Supplemental Guidance recommends an integrative 

approach that can be used to assess total lifetime risk resulting from lifetime or less-than-lifetime 

exposure during a specific portion of a lifetime. 

The following examples can help demonstrate how to apply this guidance by integrating 

potential lifestage differences in exposure and/or dose-response (potency), and also demonstrate 

what the resulting impacts are on calculated risks. These hypothetical examples consider risks 

from both lifetime, as well as less-than-lifetime oral exposures. Risks associated with inhalation 

exposure to carcinogens that act via a mutagenic mode of action are calculated in similar fashion 

by applying the appropriate ADAF(s) along with the corresponding inhalation unit risk estimate, 

using pertinent estimates of exposure concentration. 

Note again, ADAFs are only to be used for agents with a mutagenic mode of action for 

carcinogenesis when chemical-specific data are absent. For all modes of action, when chemicalspecific data are available for early-life exposure, those data should be used. 

6.1 CALCULATING LIFETIME RISKS ASSOCIATED WITH LIFETIME EXPOSURES 

Example 1: Consider a scenario of exposure to a carcinogen with a nonmutagenic mode of 

action. Suppose the oral cancer slope factor derived from a typical animal study (i.e., where 

dosing begins after puberty) is estimated to be 2 per mg/kg-d, and the exposure rate remains 

constant throughout life at 0.0001 mg/kg-d (this is equivalent to saying the daily average of 

lifetime dose rate is equal to 0.0001 mg/kg-d). The risk from lifetime exposure is calculated by 

multiplying the slope factor and the exposure rate: 

Risk = (2 per mg/kg-d) x (0.0001 mg/kg-d) 

 36
= 2 x 10-4

Example 2: Now consider the same exposure scenario for a carcinogen with a mutagenic mode 

of action for which the oral cancer slope factor, derived from a typical animal study where 

dosing begins after puberty, is also estimated to be 2 per mg/kg-d. In this case, ADAFs are used, 

as follows. 

a. To calculate lifetime risk for a population with average life expectancy of 70 years, 

sum the risk associated with each of the three relevant time periods: 

• Risk during the first 2 years of life (where the ADAF = 10); 

• Risk for ages 2 through < 16 (ADAF = 3); and 

• Risk for ages 16 until 70 years (ADAF = 1). 

Thus, risk equals the sum of: 

• Risk for birth through < 2 yr = (2 per mg/kg-d) x 10 (ADAF) x (0.0001 mg/kg-d) 

x 2yr/70yr 

= 0.6 x 10-4 

• Risk for ages 2 through < 16 = (2 per mg/kg-d) x 3 (ADAF) x (0.0001 mg/kg-d) 

 x (13yr/70yr) 

= 1.1 x 10-4 

• Risk for ages 16 until 70 = (2 per mg/kg-d) x 1 (ADAF) x (0.0001 mg/kg-d) 

 x (55yr/70yr) 

= 1.6 x 10-4

Risk = 0.6 x 10-4 + 1.1 x 10-4 + 1.6 x 10-4

= 3.3 x 10-4

b. If exposure varies with age, then such differences are also included. Now suppose the 

same example as immediately above, except that exposure for ages 1 through <12 was 

twice as high as exposure for all other ages. In this case, sum the risk associated with 

each of the five relevant time periods in which exposure rates and/or potencies (slope 

 37
factors) vary: 

Risk equals the sum of: 

• Risk for birth through < 1 yr (1yr) = (2 per mg/kg-d) x 10 (ADAF) x 0.0001 mg/kg-d 

x 1yr/70yr 

= 0.3 x 10-4

• Risk for ages 1 through < 2 (1yr) = (2 per mg/kg-d) x 10 (ADAF) x 0.0002 mg/kg-d 

x 1yr/70 yr 

= 0.6 x 10-4

• Risk for ages 2 through < 12 (10yr) = (2 per mg/kg-d) x 3 (ADAF) x 0.0002 mg/kg-d 

x 10yr/70yr 

= 1.7 x 10-4

• Risk for ages 12 through < 16 (4yr) = (2 per mg/kg-d) x 3 (ADAF) x 0.0001 mg/kg-d 

x 4yr/70yr 

= 0.3 x 10-4

• Risk for ages 16 until 70 years (55yr)= (2 per mg/kg-d) x 1 (ADAF) x 0.0001 mg/kg-d 

x 55yr/70yr 

= 1.6 x 10-4

Risk = 0.3 x 10-4 + 0.6 x 10-4 + 1.7 x 10-4 + 0.3 x 10-4 + 1.6 x 10-4

 = 4.5 x 10-4

6.2 CALCULATING LIFETIME RISKS ASSOCIATED WITH LESS THAN LIFETIME 

EXPOSURES 

If exposure only occurs for a limited number of years (for example, consider a family that 

lives near a source of exposure for a five-year period of time before moving away), it is critical 

to combine lifestage differences in exposure and dose-response for the relevant time interval. 

The examples presented below demonstrate how adjusting potency and/or exposure can affect 

the assessment of cancer risk. 

 38
Example 3: If exposure to a carcinogen with a mutagenic mode of action with an oral slope 

factor equal to 2 per mg/kg-d occurs during adulthood for only 5 years, the daily average of 

lifetime dose is time weighted to apportion risk for the number of years of exposure by a factor 

of 5/70: 

Risk = (2 per mg/kg-d) x (0.0001 mg/kg-d) x (5yr/70yr) 

= 1.4 x 10-5

Example 4: If this 5-year exposure occurs during childhood, the risk calculations are adjusted to 

consider the potential for higher potency from early-life exposure. Assessors should remember 

that the age dependent adjustment factors for carcinogens with a mutagenic mode of action are 

applied only to exposure periods occurring up to age 16. 

a. For a child exposed between ages 5 and 10, only a 3-fold ADAF is applied because 

the exposure occurs entirely between ages 2 and <16 years: 

Risk = 3 (ADAF) x (2 per mg/kg-d) x (0.0001 mg/kg-d) x (5 yr/70 yr) 

= 4.3 x 10-5

b. For an exposure between ages 13 and <18, a 3-fold ADAF is applied only to the 

3-year portion occurring before age 16: 

Risk equals the sum of: 

• Risk for ages 13 through < 16 (3yr) = 3 (ADAF) x (2 per mg/kg-d) x (0.0001 mg/kg-d) 

x (3 yr/70 yr) 

= 2.6 x 10-5

• Risk for ages 16 through < 18 (2yr) = 1 (ADAF) x (2 per mg/kg-d) x (0.0001 mg/kg-d) 

x (2 yr/70 yr) 

= 0.6 x 10-5

Risk = 2.6 x 10-5 + 0.6 x 10-5 

 39
= 3.2 x 10-5

c. For a child exposed from birth through age 5, different ADAFs are applied to the 

periods before and after age 2: 

Risk equals the sum of: 

• Risk for birth through < 2 (2yr) = 10 (ADAF) x (2 per mg/kg-d) x (0.0001 mg/kg-d) 

x (2 yr/70 yr) 

= 5.7 x 10-5

• Risk for ages 2 through < 5 (3yr) = 3 (ADAF) x (2 per mg/kg-d) x (0.0001 mg/kg-d) 

x (3 yr/70 yr) 

= 2.6 x 10-5

Risk = 5.7 x 10-5 + 2.6 x 10-5 

= 8.3 x 10-5

Example 5: Lifetime risk calculations based on less-than-lifetime exposure to a carcinogen with 

a mutagenic mode of action include any lifestage changes in potency as well as exposure. In this 

example, again consider a scenario of 5 years of exposure to a carcinogen with a mutagenic 

mode of action, but suppose that the exposure rate is found to vary from 0.0002 mg/kg-d during 

the first 2 years of life, to 0.0001 mg/kg-d during the last 3 years. 

a. For a child exposed between birth and age 5, sum the risk associated with the two 

relevant time periods: 

Risk equals the sum of: 

 40
• Risk for birth through < 2 (2yr) = 10 (ADAF) x (2 per mg/kg-d) x (0.0002 mg/kg-d) 

x (2 yr/70 yr) 

= 11.4 x 10-5

• Risk for ages 2 through < 5 (3yr) = 3 (ADAF) x (2 per mg/kg-d) x (0.0001 mg/kg-d) 

x (3 yr/70 yr) 

= 2.6 x 10-5

Risk = 11.4 x 10-5 + 2.6 x 10-5 

= 1.4 x 10-4

b. For comparison, a similar risk calculation for 5 years of exposure later in life (after 

age 16) in which the first 2 years of exposure are double that of the next 3 years are 

carried out without any adjustment for potency: 

Risk equals the sum of: 

• Risk for first 2 years of adult exposure = 1 (ADAF) x (2 per mg/kg-d) 

x (0.0002 mg/kg-d) x (2yr/70yr) 

= 1.1 x 10-5

• Risk for final 3 years of adult exposure = 1 (ADAF) x (2 per mg/kg-d) 

x (0.0001 mg/kg-d) x (3yr/70yr) 

= 0.9 x 10-5

Risk = 1.1 x 10-5 + 0.9 x 10-5

= 2 x 10-5

 41
Standard Rodent Cancer Study: Adult Exposur

In

ute

r

o

&

p

o

stn

atal E

x

p

o

s

u

r

e

Postnatal & Adult Exposure (Lifetime)

In utero, postnatal, & Adult Exposure (Lifetime) 

Postnatal Exposure 

birth 

mating weaning 

puberty As

o

Figure 1. Study designs.

42
Acute 

Exposures

Repeated or 

Lifetime 

Exposures 

Figure 2: Posterior, unweighted geometric means and 95% confidence intervals for the ratios of juvenile to 

adult cancer potency for carcinogens acting primarily through a mutagenic mode of action. The top panel is

for repeated and lifetime exposure studies (geometric mean in black), the bottom panel is for acute exposure studies 

mutagens (geometric mean in white). The horizontal lines to the left and right of each geometric mean correspond to 

95% confidence limits. The vertical dark line represents the inverse-variance weighted geometric mean of the 

posterior geometric means. The horizontal dark line represents the 95th percentile of the unweighted distribution,

with the vertical, dotted line establishing it value. 
Box 1: Use framework in Cancer Guidelines

to establish MOA(s)

Figure 3. Flow chart for early-life risk assessment using mode of action framework

MOA sufficiently 

supported in animals?

MOA relevant to

humans?

Flag lifestage(s) or population(s) that

could be susceptible (based on

information about the specific MOA)

for dose-response analysis.

Box 2: Use linear

extrapolation as a default.

Determine extrapolation

based on information 

about specific MOA.

Box 3: Model using MOA or

use RfD/RfC method as default. 

Adjustments for susceptible

lifestages or populations are part

of the process.

No

Linearity due to

mutagenic MOA

MOA can not

be determined

Nonlinear

Yes

Yes

Linear, but

nonmutagenic

MOA Box 4: Use the same linear

extrapolation for all lifestages,

unless have chemical-specific 

information on lifestages or

populations.

Were chemical-specific data available

in MOA analysis to evaluate differences

between adults and juveniles (more,

less, or the same susceptibility)?

Box 5: Develop chemicalspecific risk estimates 

incorporating lifestage

susceptibility.

Yes

Box 6: Early-life susceptibility assumed. Apply

age-dependent adjustment factors (ADAFs) as

appropriate to develop risk estimates.

No 

Supplemental Guidance for Early-Life Exposures

No further analysis of

tumors.
Table 1a. Chemicals that have been found to have carcinogenic effects from prenatal or postnatal e

animals as identified in different review articles 

A-1

Chemical name 

Review articles including prenatal and postnatal exposu

Fujii (1991) 

McClain 

et al. 

(2001) 

Anderson 

et al. 

(2000) 

Della Porta 

and 

Terracini 

(1969) 

Othe

literat

4-Acetylaminobiphenyl (AAB) X 4-Aminoazobenzene (AB) X 3-Amino-1,4,-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) X 2-Aminodipyridol[1,2-a:3',2'-d]imidazole (Glu-P-2) X 2-Amino-6-methyldipyridol[1,2-a:3',2'-d]imidazole (Glu-P-1) X 3-Amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) X Amitrole Arsenic X 5-Azacytidine X 3'-Azido-3'-deoxythymidine (AZT) X Azoxymethane X Benz[a]anthracene X Benzidine X Benzo[a]pyrene (BaP) X X 1­ (4'Bromophenylazo)-1-phenyl-1-hydroperoxymethane (BPH) X N-Butyl-N-(3-carboxypropyl)nitrosamine (BCPN) X N-Butyl-N-(3 hydroxbutyl)nitrosamine (BBN) X Butylnitrosourea (BNU) X Cyclophosphamide X Dibenz[a,h]anthracene (DBA) X Dibutylnitrosamine (DBN) X Dichlorodiphenyltrichloroethane (DDT) Dieldrin 2-Diethylaminoethyl-2,2-dephenylvalerate hydrochloride (SKF 525A) X 
Table 1a. Chemicals that have been found to have carcinogenic effects from prenatal or postnatal e

animals as identified in different review articles (continued) 

Chemical name 

Review articles including prenatal and postnatal exposu

Fujii (1991) 

McClain 

et al. 

(2001) 

Anderson 

et al. 

(2000) 

Della Porta 

and 

Terracini 

(1969) 

Othe

literat

Diethylnitrosamine (DEN) X X Diethylstilbesterol (DES) X 4-Dimethylaminoazobenzene X 1,2-Dimethylhydrazine (DMH) X 7,12-Dimethylbenz[a]anthracene (DMBA) X X X Dimethylnitrosamine (DMN) X X X 5',5'-Diphenylhydantoin (DPH) Estradiol X X 6-Ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (Santoquin) X Ethylene thiourea (ETU) Ethyl methane sulphonate X Ethylnitrosobiuret X Ethylnitrosourea (ENU) X N-2-Fluorenylacetamide (FAA) X X Genistein X 3-Hydroxyl-4-acetylaminobiphenyl (N-OH-AAB) X N-2-Hydroxy-N-2-fluorenylacetamide (N-OH-FAA) X 2-Hydroxypropyl-propylnitrosamine X 9-Methylanthracene X Methyl-2-benzylhydrazine X Methylcholanthrene X X 3-Methyl-4-dimethylaminoabenzene (3'ME-DAB) X 4-(Methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK) X Methylnitrosourea (NMU) X Methylnitrosourethane X 1-Methyl-3-nitro-1-nitrosoguanidine (MNNG) X 

A-2 
Table 1a. Chemicals that have been found to have carcinogenic effects from prenatal or postnatal e

animals as identified in different review articles (continued) 

Chemical name 

Review articles including prenatal and postnatal exposu

Fujii (1991) 

McClain 

et al. 

(2001) 

Anderson 

et al. 

(2000) 

Della Porta 

and 

Terracini 

(1969) 

Othe

literat

2-Naphthylamine X 2-Naphthylhydroxyamine X Nickel acetate X N-Nitrosobuylamine X 4-Nitroquinoline-1-oxide X X N-Nitrosomethyl(2-oxopropyl)amine X 2-Oxopropyl-propylnitrosamine X 1-Phenyl-3,3',-dimethylhydrzine X 1-Phenyl-3,3,-dimethyltriazene X Polybrominated biphenyls (PBBs) Safrole (3,4-methylenedioxyally benzene) X X Soot X Sterigmatocystin X Tamoxifen X 1,3,5-Trimethyl-2,4,6-tris[3,5-di-tert-butyl-4-hydroxybenzyl]benzene (Ionox 33) X Urethane (ethyl carbamate) X X Vinyl chloride 

A-3 
Table 1b. List of chemicals considered in this analysis. (These are chemicals 

for which both early-life and adult exposure are reported in the same animal 

experiment.) 

Chemical References Study type 

Mutagenic 

mode of action 

Amitrole Vesselinovitch (1983) Repeat dosing 

Benzidine Vesselinovitch et al. (1975b) Repeat dosing X 

Benzo[a]pyrene (BaP) Vesselinovitch et al. (1975a) Acute exposure X 

Dibenzanthracene (DBA) Law (1940) Acute exposure X 

Dichlorodiphenyltrichloroethane Vesselinovitch et al. (1979) Repeat dosing 

(DDT) Lifetime exposure 

Dieldrin Vesselinovitch et al. (1979) Repeat dosing 

Lifetime exposure 

Diethylnitrosamine (DEN) Peto et al. (1984) Lifetime exposure X 

Vesselinovitch et al. (1984) Acute exposure 

Dimethylbenz[a]anthracene 

(DMBA) 

Meranze et al. (1969) Acute exposure X 

Pietra et al. (1961) Acute exposure 

 Walters (1966) Acute exposure 

Dimethylnitrosamine (DMN) Hard (1979) Acute exposure X 

Diphenylhydantoin, 5,5- (DPH) Chhabra et al. (1993b) Repeat dosing 

Lifetime exposure 

Ethylnitrosourea (ENU) Naito et al. (1981) Acute exposure X 

Vesselinovitch et al. (1974) Acute exposure 

Vesselinovitch (1983) Acute exposure 

Ethylene thiourea (ETU) Chhabra et al. (1992) Repeat dosing 

Lifetime exposure 

3-Methylcholanthrene (3-MU)a Klein (1959) Repeat dosing X 

Methylnitrosourea (NMU) Terracini and Testa (1970) Acute exposure X 

Terracini et al. (1976) Acute exposure 

Polybrominated biphenyls Chhabra et al. (1993a) Repeat dosing 

(PBBs) Lifetime exposure 

Safrole Vesselinovitch et al. (1979) Repeat dosing 

Lifetime exposure 

X 

Urethane Chieco-Bianchi et al. (1963) 

Choudari Kommineni et al. (1970) 

Acute exposure 

Acute exposure 

X 

De Benedictis et al. (1962) Acute exposure 

Fiore-Donati et al. (1962) Acute exposure 

 Klein (1966) Acute exposure 

Lifetime exposure 

Liebelt et al. (1964) Acute exposure 

 Rogers (1951) Acute exposure 

Vinyl chloride (VC) Maltoni et al. (1984) Repeat dosing X 

a

 Formerly known as 20-methylcholanthrene. 

A-4 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures 

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M F 

Amitrole Mice liver Control None Control: N/A 90 weeks 1/98 0/96 In

(B6C3F1) 0 ppm (1%) (0%) m

Gestation day 12 

Diet, to mothers 

500 ppm Gestation day 

12 to delivery 

6/74 

(8%)b 

0/83 

(0%)b 

adca

Newborn Diet, to 

mothers 

500 ppm Birth until 

weaning 

10/45 

(22%)b 

0/55 

(0%)b 

At weaning Diet, to 

offspring 

500 ppm From weaning 

to 90 weeks 

20/55 

(36%)b 

9/49 

(18%)b 

Benzidine Mice liver Control None Control: N/A 90 weeks 1/98 0/100 H

(B6C3F1) 0 ppm (1%) (0%) se

Gestation day 12 

Diet, to mothers 

150 ppm Gestation day 

12 to delivery 

17/55 

(31%)c 

2/62 

(3%)d 

mpepe

A-5 

Newborn Diet, to 

mothers 

150 ppm Birth until 

weaning 

62/65 

(95%)c 

2/43 

(5%)d 

fead

At weaning Diet, to 

offspring 

150 ppm From weaning 

to 90 weeks 

22/50 

(44%)c 

47/50 

(94%)c In

m

Gestation day 12 

Diet, to mothers 

150 ppm Gestation day 

12 until 

49/49 

(100%)c 

12/48 

(25%)c 

adca

weaning 

Gestation Diet, to 150 ppm Gestation day 50/50 47/50 day 12 mothers 12 until 90 (100%)c (94%)c 

weeks 

DDT Mice liver Control None Control: N/A 90 weeks 1/50 — Dichlorodiphenyl­ (B6C3F1) 0 ppm (2%) trichloroethane 

Week 1 Gavage, 

daily 

230 μg Weeks 1–4 5/49 

(10%)d 

— 

Week 5 Diet, 

daily 

150 ppm Weeks 5–90 8/49 

(16%)d 

— 

Week 1 Gavage, 230 μg Weeks 1–90 10/50 — 

daily until (20%)c 4 weeks, 150 ppm then in (diet) diet 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

Dose Tumorsa Species Target Age when Duration of Age at route, Chemical (strain) site first dosed Dose exposure death M 

# doses 

F

Dieldrin Mice liver Control None Control: N/A 1/58 — 

(B6C3F1) 

90 weeks 

0 ppm (2%) 

Week 1 Gavage, 12.5 μg Weeks 1–4 3/46 — 

daily (7%)b 

Week 5 Diet, 10 ppm Weeks 5–90 7/60 — 

daily (12%)b 

Week 1 Gavage, 12.5 μg Weeks 1–90 21/70 — 

daily until (30%)a 

4 weeks, 10 ppm 

then in diet 

DENe Rats liver Control Control N/A 29/384 H

Diethylnitrosamine (Colworth) (8%) ra

at 

Week 3 From week 3 6 105/180 

drinking 

Diet (in 16 different 

until death months– (58%)b doses In

water), combinedf 3 years radaily ad

until death 

Week 6 From week 6 714/1440 

(50%) ca

b 

Week 20 From week 20 76/180 

until death (42%)b 

esophagus Control Control N/A 0/384 

(0%) 

Week 3 Diet (in From week 3 77/180 

drinking 

16 different doses until death (43%)b 

water), combinedg Week 6 From week 6 663/1440 daily until death (46%)b 

Week 20 From week 20 88/180 

until death (49%)b 

A-6 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-7

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

DPH Rats liver Control Control 0 ppm N/A 2 years 0/50 0/50 In raDiphenylhydantoin, (F344/N) (0%) (0%) expo5,5- Perinatal Diet, 

daily 

630 ppm Perinatal 

through 8 weeks 

1/50 

(2%)d 

0/49 

(0%)d 

from ppmexpofrom ppm

8 weeks 800 ppm 8 weeks–2 

years 

2/50 

(4%)d 

1/50 

(2%)d 

8 weeks 2,400 ppm 8 weeks–2 

years 

4/50 

(8%)d 

1/50 

(2%)d 

In mexpofrom ppmexpofrom ppm 

Perinatal 630–800 Perinatal 

through 2 years 

1/49 

(2%)d 

0/50 

(0%)d 

Perinatal 630–2,400 

ppm 

Perinatal through 2 years 

5/49 

(10%)c 

0/50 

(0%)d 

Mice (B6C3F1) 

liver Control Control 

male 

0 ppm N/A 2 years 29/50 

(58%) 

60 to femaTumare aadencarci

Perinatal Diet, male 210 ppm Perinatal 

through 8 weeks 

33/50 

(66%)d 

8 weeks 100 ppm 8 weeks–2 

years 

29/49 

(59%)d 

8 weeks 300 ppm 8 weeks–2 

years 

26/49 

(53%)d 

Perinatal 210–100 

ppm 

Perinatal through 2 years 

35/49 

(71%)d 

Perinatal 210–300 Perinatal 41/50 

ppm through 2 years (82%)c

 Control Control 

female 

0 ppm N/A 2 years 5/48 

(10.4%)d 

Perinatal Diet, 

female 

210 ppm Perinatal 

through 8 

12/49 

(24.5%)d 

weeks 

8 weeks 200 ppm 8 weeks–2 14/49 

years (28%)c 

8 weeks 600 ppm 8 weeks–2 30/50 

years (60%)c 

Perinatal 210–200 Perinatal 16/50 

ppm through 2 years (32%)c 

Perinatal 210–600 Perinatal 34/50 

ppm through 2 years (68%)c 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-8

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

ETU Rats thyroid Control Control 0 ppm N/A 2 years 1/49 3/50 TumEthylene thiourea (F344/N) (2%) (6%) are a

Perinatal Diet, 

daily 

90 ppm Perinatal 

through 8 

4/49 

(8%)d 

3/50 

(6%)d 

adencarci

weeks 

8 weeks 83 ppm 8 weeks–2 

years 

12/46 

(26%)c 

7/44 

(16%)d 

8 weeks 250 ppm 8 weeks–2 37/50 30/49 

years (74%)c (61%)c

 Perinatal 90–83 ppm Perinatal 

through 2 years 

13/50 

(26%)c 

9/47 

(19%)d 

Perinatal 90–250 ppm Perinatal 48/50 37/50 

through 2 years (96%) (74%)

 Mice 

(B6C3F1) 

liver Control Control 0 ppm N/A 2 years 20/49 

(41%) 

4/50 

(8%) 

Perinatal Diet, 

daily 

330 ppm Perinatal 

through 8 

13/49 

(26.5%)d 

5/49 

(10%)d 

weeks 

8 weeks 330 ppm 8 weeks–2 32/50 44/50 

years (64%)c (88%)c 

8 weeks 1,000 ppm 8 weeks–2 46/50 48/50 

years (92%)c (96%)c 

Perinatal 330–330 Perinatal 34/49 46/50 

ppm through 2 years (69%)c (92%)c

 Perinatal 330–1,000 Perinatal 47/49 49/50 

ppm through 2 years (6%)c (98%)c 

thyroid Control Control 0 ppm N/A 1/50 

(2%) 

0/50 

(0%) 

Perinatal Diet, 

daily 

330 ppm Perinatal 

through 8 

1/46 

(2%)d 

1/49 

(2%)d 

weeks 

8 weeks 330 ppm 8 weeks–2 

years 

1/49 

(2%)d 

2/50 

(4%)d 

8 weeks 1,000 ppm 8 weeks–2 29/50 38/50 

years (58%)c (76%)c 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-9

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

ETU Ethylene thiourea 

 Perinatal 330–330 

ppm 

Perinatal through 2 years 

2/48 

(4%)d 

10/49 

(20%)c

(continued)

 Perinatal 330–1,000 Perinatal 35/49 38/50 

ppm through 2 years (71%)c (76%)c 

pituitary Control Control 0 ppm N/A 0/44 

(0%) 

11/47 

(23%) 

Perinatal Diet, 

daily 

330 ppm Perinatal 

through 8 

0/42 

(0%)d 

11/48 

(23%)d 

weeks 

8 weeks 330 ppm 8 weeks–2 

years 

0/42 

(0%)d 

19/49 

(39%)d 

8 weeks 1,000 ppm 8 weeks–2 8/41 26/49 

years (19.5%)c (53%)c 

Perinatal 330–330 

ppm 

Perinatal through 2 years 

0/45 

(0%)d 

26/47 

(55%)c 

Perinatal 330–1,000 

ppm 

Perinatal through 2 years 

4/39 

(10%)d 

24/47 

(51%)c 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-10

Age Age at death Tumor i

Chemical 

Species 

(strain) 

Target 

site 

when 

first 

dosed 

Dose route, 

# doses Dose 

Duration of 

exposure M F M 

3-Methylcholanthrene Mice liver Control gavage, 3× NA NA 475 days 480 days 3/39 (formerly known as 20- (Albino) per week (7.7%) methylcholanthrene) 8 days 0.25 mg/g 10× 311 days 321 days 21/25 

(84%)b 

90 days 0.25 mg/g 10× 330 days 366 days 1/26 

(3.8%)b 

lung Control NA NA 475 days 480 days 17/39 

(43.6%) 

8 days 0.25 mg/g 10× 311 days 321 days 25/25 

(100%)b 

90 days 0.25 mg/g 10× 330 days 366 days 25/26 

(96.2%)b 

forestomach Control NA NA 475 days 480 days 0/39 (0%) 

8 days 0.25 mg/g 10× 311 days 321 days 12/25 

(48%)b 

90 days 0.25 mg/g 10× 330 days 366 days 13/26 

(50%)b 

skin Control NA NA 475 days 480 days 0/39 

(0%) 

8 days 0.25 mg/g 10× 311 days 321 days 4/25 

(16%)b 

90 days 0.25 mg/g 10× 330 days 366 days 1/26 

(3.8%)b 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-11

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M 

F 

PBBs Rats (F344/N) liverg Control Control 0 ppm N/A 2 years 1/50 0/50 Polybrominated (2%) (0%) biphenyls Perinatal Diet 10 ppm Perinatal–8 

weeks 

5/50 

(10%)d 

0/50 

(0%)d 

8 weeks 10 ppm 8 weeks–2 

years 

12/49 

(24%)c 

12/50 

(24%)c 

8 weeks 30 ppm 8 weeks–2 

years 

41/50 

(82%)c 

39/50 

(78%)c 

Perinatal 10–10 ppm Perinatal–2 16/50 39/50 

years (32%)c (78%)c 

Perinatal 10–30 ppm Perinatal–2 

years 

41/50 

(82%)c 

47/50 

(94%)c 

Mononuclear cell leukemia (MCL) 

Control Control 0 ppm N/A 2 years 25/50 

(50%) 

14/50 

(28%) 

Perinatal Diet 10 ppm Perinatal–8 

weeks 

31/50 

(62%)d 

13/50 

(26%)d 

8 weeks 10 ppm 8 weeks–2 

years 

33/50 

(66%)c 

22/50 

(44%)d 

8 weeks 30 ppm 8 weeks–2 

years 

31/50 

(62%)d 

23/50 

(46%)c 

Perinatal 10–10 ppm Perinatal–2 

years 

37/50 

(74%)c 

27/50 

(54%)c 

Perinatal 10–30 ppm Perinatal–2 37/50 25/50 

years (74%)c (50%)c 

Mice (B6C3F1) liverg Control Control 0 ppm N/A 2 years 16/50 

(32%) 

5/50 

(10%) 

Perinatal Diet 30 ppm Perinatal–8 40/50 21/50 

weeks (80%)c (42%)c 

8 weeks 10 ppm 8 weeks–2 48/49 42/50 

years (98%)c (84%)c 

8 weeks 30 ppm 8 weeks–2 48/50 47/48 

years (96%)c (98%)c 

Perinatal 10 ppm Perinatal–2 46/49 44/50 

years (94%)c (88%)c 

Perinatal 30–30 ppm Perinatal–2 50/50 47/47 

years (100%)c (100%)c 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-12

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M 

F 

Safrole Mice liver Control None None N/A 90 weeks 3/100 0/100 

(B6C3F1) (3%) (0%) 

Day 12 of gestation 

Gavage, to mothers 

120 μg/g body weight 

4× (days 12, 14, 16, 18) 

2/61 

(3%)d 

0/65 

(0%)d 

Newborn Gavage, to 

mothers, on 

120 μg/g body weight 

From birth until weaning 

28/83 

(34%)c 

2/80 

(3%)d 

alternate days 

At weaning Gavage, to 

offspring, 2× weekly 

120 μg/g body weight 

From weaning until 90 weeks 

4/35 

(11%)d 

22/36 

(61%)c 

Day 12 of gestation 

Gavage, to mothers, alternate days 

120 μg/g body weight 

From gestation until weaning 

22/68 

(32%)b 

1/72 

(1%)b 

Day 12 of gestation 

Gavage, to mothers, alternate 

120 μg/g body weight 

From gestation until 90 weeks 

19/37 

(51%)b 

37/46 

(80%)b 

days until weaning; Gavage, to offspring, 2× weekly 

Urethane Mice (B6AF1/J) liver 1 week gavage 2.5 mg/pup 1× 39–40 

weeks 

Tumor incidencea 

M F 

12/37 

(33%)b 

0/40 

(0%)b 

1 week 2.5 mg/pup 16× 

(1× at 1 week; 3× weekly for 5 weeks 

39 weeks 11/33 

(33%)b 

0/31 

(0%)b 

beginning at 4 wks of age) 

4 weeks 2.5 mg/pup 15× 

(3× weekly for 5 weeks 

41 weeks 0/37 

(0%)b 

0/31 

(0%)b 

beginning at 4 weeks of age) 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

Dose Tumorsa Species Target Age when Duration of Age at route, Chemical (strain) site first dosed Dose exposure death M 

# doses 

F

VC Rats (Sprague­ liver Control Control 0 ppm N/A 135 0/22 0/29 

Vinyl chloride Dawley) angio­ weeks (0%) (0%) 

sarcoma 

Newborn Inhalation 6,000 ppm 4 hrs/day, 124 5/18 12/24 

5 days/wk, weeks (28%)b (50%)b 5 weeks 10,000 ppm 6/24 9/20 

(25%)b (45%)b

Week 13 6,000 ppm 4 hrs/day, 135 3/17 10/25 

5 days/wk, 52 weeks (18%)b (40%)b 

weeks 4/25 

(14%)b

 10,000 ppm 3/21 

(16%)b 

zymbal Control Control 0 ppm N/A 135 0/28 0/29 

gland weeks (0%) (0%) 

Newborn Inhalation 6,000 ppm 4 hrs/day, 124 1/12 1/17 

5 days/wk, weeks (8%)b (6%)b

5 weeks 10,000 ppm 1/17 0/17 

(6%)b (0%)b 

Week 13 6,000 ppm 4 hrs/day, 135 3/29 4/30 

5 days/wk, 52 (13%)b 

weeks 

weeks (10%)b 

 10,000 ppm 10/30 6/30 

(33%)b (20%)b 

leukemia Control Control 0 ppm N/A 135 0/27 1/29 

weeks (0%) (3%) 

Newborn Inhalation 6,000 ppm 4 hrs/day, 124 N/A 1/7 

5 days/wk, weeks (14%)b

5 weeks 10,000 ppm 2/6 0/15 

(33%)b (0%)b 

Week 13 6,000 ppm 4 hrs/day, 135 N/A 0/29 

5 days/wk, 52 weeks (0%)bweeks 10,000 ppm 0/27 2/29 

(0%)b (7%)b 

nephro- Control Control 0 ppm N/A 135 0/22 0/29 

blastoma weeks (0%) (0%) 

Newborn Inhalation 6,000 ppm 4 hrs/day, 124 0/15 0/21 

5 days/wk, weeks (0%)b (0%)b

5 weeks 10,000 ppm 0/19 0/17 

(0%)b (0%)b 

A-13 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

A-14

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M 

F 

VC Vinyl chloride 

Week 13 6,000 ppm 4 hrs/day, 

5 days/wk, 52 

135 

weeks 

4/18 

(22%)b 

1/26 

(4%)b

(continued) weeks 

 10,000 ppm 3/21 

(14%)b 

2/25 

(8%)b 

angio- Control Control 0 ppm N/A 135 0/29 0/29 sarcomas: weeks (0%) (0%) other sites Newborn Inhalation 6,000 ppm 4 hrs/day, 

5 days/wk, 

124 

weeks 

1/15 

(7%)b 

0/21 

(0%)b

 10,000 ppm 5 weeks 0/19 

(0%) 

0/17 

(0%)b 

Week 13 6,000 ppm 4 hrs/day, 

5 days/wk, 52 

135 

weeks 

1/29 

(3%)b 

2/30 

(7%)b 

 10,000 ppm weeks 2/30 

(7%)b 

1/30 

(3%)b 

angiomas and 

Control Control 0 ppm N/A 135 

weeks 

0/28 

(0%) 

2/29 

(7%)b 

fibromas: other sites Newborn Inhalation 6,000 ppm 4 hrs/day, 5 days/wk, 124 weeks 1/15 (7%)b 0/21 (0%)b

 10,000 ppm 5 weeks 2/19 

(11%)b 

1/17 

(6%)b 

Week 13 6,000 ppm 4 hrs/day, 

5 days/wk, 52 

135 

weeks 

2/29 

(7%)b 

2/30 

(7%)b 

 10,000 ppm weeks 2/29 

(7%)b 

1/29 

(3%)b

 hepatoma Control Control 0 ppm N/A 135 

weeks 

0/19 

(0%) 

0/28 

(0%) 

Newborn Inhalation 6,000 ppm 4 hrs/day, 

5 days/wk, 

124 

weeks 

9/18 

(50%)b 

11/24 

(46%)b

 10,000 ppm 5 weeks 13/24 

(54%)b 

7/20 

(35%)b 

Week 13 6,000 ppm 4 hrs/day, 

5 days/wk, 52 

135 

weeks 

0/10 

(0%)b 

1/17 

(6%)b

 10,000 ppm weeks 1/8 

(13%)b 

0/16 

(0%)b 
Table 2. Methodological information and tumor incidence for animal studies with early postnatal a

and adult repeated exposures (continued) 

Dose Tumorsa Species Age when Duration of Age at route, Chemical (strain) Target site first dosed Dose exposure death 

# doses M F 

VC Control skin Control 0 ppm N/A 135 0/20 1/29 

Vinyl chloride carcinomas weeks (0%) (3%) (continued) Newborn Inhalation 6,000 ppm 4 hrs/day, 124 1/10 1/14 

5 days/wk, (7%)b

5 weeks 

weeks (10%)b 

 10,000 ppm 0/15 

(6%)b

1/16 

(0%)b 

Week 13 6,000 ppm 4 hrs/day, 135 0/15 2/19 

5 days/wk, 52 (11%)b 

weeks 

weeks (0%)b 

 10,000 ppm 1/21 

(15%)b

2/13 

(5%)b 

neuro- Control Control 0 ppm N/A 135 0/22 0/29 

blastoma weeks (0%) (0%) 

Newborn Inhalation 6,000 ppm 4 hrs/day, 124 0/18 0/29

5 days/wk, weeks (0%)b (0%)b

A-15 10,000 ppm 5 weeks 0/22 (0%)b 0/19 (0%)b Week 13 6,000 ppm 4 hrs/day, 

5 days/wk, 52 

135 

weeks 

2/21 

(10%)b 

1/27 

(4%)b 

 10,000 ppm weeks 2/22 

(9%)b 

5/26 

(19%)b 

a Where not delineated by gender, data combined by study authors or gender not specified. Where percentages only are given, number ob Not evaluated by authors. c Significant compared with controls. d Evaluated but not significant compared with controls. e Reported as NDEA (N-nitrosodiethylamine) in the original document. f Results from each dose are not available. g Tumors were adenomas or carcinomas. 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure 

A-16

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M Co

F 

BaP Mice liver Control Control None N/A 142 weeks 7/100 1/100 In generalBenzo[a]pyrene (B6C3F1) (7%) (1%) developed 

Day 1 i.p. 75 μg/g 

body weight 

1× 86 weeks 

(m) 129 weeks (f) 

26/47 

(55%)b 

3/45 

(7%)b 

significanincidence mice that within 24 or at 15 d

150 μg/g body weight 

1× 81 weeks 

(m) 121 weeks 

51/63 

(81%)b 

8/45 

(18%)b 

than they similarly animals a

(f) age. 

+ higher f

Day 15 i.p. 75 μg/g body weight 1× 93 weeks (m) 

116 weeks (f) 

36/60 

(60%)b 

4/55 

(7%)b 

150 μg/g body weight 

1× 81 weeks 

(m) 

32/55 

(58%)b 

4/55 

(7%)b 

90 weeks (f) 

Day 42 i.p. 75 μg/g 

body weight 

1× 108 

weeks(m) 

7/55 

(13%)b 

0/47 

(0%)b 

150 μg/g body weight 

1× 87 weeks 

(m) 

4/47 

(9%)b 

0/46 

(0%)b 

Mice liver Control Control None N/A 142 weeks 8/100 1/100 + higher f

(C3AF1) (8%) (1%) 

Day 1 i.p. 75 μg/g 

body weight 

1× 80 weeks 

(m) 91 weeks (f) 

21/62 

(34%)b 

1/45 

(2%)b 

“Age at daverage atumors we

150 μg/g body weight 

1× 69 weeks 

(m) 

24/52 

(46%)b 

1/56 

(2%)b 

701 weeks (f) 

Day 15 i.p. 75 μg/g 

body weight 

1× 90 weeks 

(m) 

15/56 

(27%)b 

1/49 

(2%)b 

102 weeks (f) 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-17

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M Co

F 

BaP Benzo[a]pyrene 

150 μg/g 

body weight 

1× 77 weeks 

(m) 

12/53 

(23%)b 

1/57 

(2%)b 

(continued) 62 weeks (f) 

Day 42 i.p. 75 μg/g 

body weight 

1× 0/30 

(0%)b 

0/32 

(0%)b 

150 μg/g body weight 

1× 79 weeks 

(m) 

1/32 

(3%)c 

0/40 

(0%)b 

Mice lung Control Control Control N/A 142 weeks 13/100 9/100 Both sexe

(B6C3F1) (13%) (9%) lung tumo

Day 1 i.p. 75 μg/g 

body weight 

1× 103 weeks 

(m) 126 weeks (f) 

20/47 

(43%)b 

22/45 

(49%)b 

incidence with BaP 15 or 42 d(p<0.05). 

150 μg/g body weight 

1× 84 weeks 

(m) 

37/63 

(59%)b 

28/45 

(62%)b 

112 weeks (f) 

Day 15 i.p. 75 μg/g 

body weight 

1× 103 weeks 

(m) 

15/60 

(25%)b 

18/55 

(33%)b 

122 weeks (f) 

150 μg/g body weight 

1× 82 weeks 

(m) 

20/55 

(36%)b 

18/45 

(40%)b 

101 weeks (f) 

Day 42 i.p. 75 μg/g 

body weight 

1× 119 weeks 

(m) 

20/55 

(36%)b 

12/47 

(26%)b

131 weeks (f) 

150 μg/g body weight 

1× 95 weeks 

(m) 

18/47 

(38%)b 

8/46 

(17%)b 

118 weeks (f) 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Tumorsa Dose Species Target Age when Duration of Age at route, Chemical (strain) site first dosed Dose exposure death Com

# doses M F 

BaP Mice lung Control Control None N/A 142 weeks 60/100 50/100 

Benzo[a]pyrene 

Of the tw

(C3AF1) (60%) (50%) strains tes

(continued) mice deve

Day 1 i.p. 75 μg/g 1× 78 weeks 58/62 42/45 significan

body weight (m) (93%)b (93%)b tumors th

82 weeks (f) B6C3F1 m

150 μg/g (p<0.001)

body weight 

1× 70 weeks 48/52 52/56 

(m) (92%)b (93%)b 73 weeks (f) 

75 μg/g 1× 87 weeks 46/49 

body weight 

Day 15 i.p. 52/56 

(m) (93%)b (94%)b 98 weeks (f) 

150 μg/g 1× 75 weeks 50/53 52/57 

body weight (m) (94%)b (91%)b 

79 weeks (f) 

Day 42 i.p. 75 μg/g 1× 91 weeks 28/30 28/32 

body weight (m) (93%)b (87%)b 

93 weeks (f) 

150 μg/g 1× 85 weeks 28/32 36/40 

body weight (m) (87%)b (90%)b 

83 weeks (f) 

DBA Mice lung Control Control None N/A 228 days 1/31 

Dibenzanthracene (Caracul × P (3.2%) 

stock) Day 1 i.p. 4 mg per 1× 181 days 24/24 

cm3 vehicle (100%)b 

2 months s.c. 4 mg per 1× 189 days 2/29 

cm3 vehicle (6.9%)b

A-18 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-19

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M Comm

F 

DEN Diethylnitrosamine 

Mice (B6C3F1) 

liver Control Control Vehicle 

(0.01 mL trioctanoin/g 

4× 142 

weeks (m) 

7/98 

(7%) 

1/100 

(1%) 

Animals treanewborns andeveloped si

body weight) 137 more liver tu

weeks (f) animals that 

treated as yoNewborns anfemales devetumors at a l

Day 1 i.p. (3-, 6­

and 6-day intervals) 

1.5 μg/g body weight 

4× 67 weeks 

(m) 90 weeks (f) 

37/51 

(73%)b 

45/64 

(70%)b 

3 μg/g body weight 

4× 65 weeks 

(m) 80 weeks 

40/58 

(69%)b 

44/65 

(68%)b 

than similarlmales. 

(f) Incidences fo

malignant tu

Day 15 1.5 μg/g 

body weight 

4× 86 weeks 

(m) 

41/57 

(72%)b 

40/71 

(56%)b 

117 weeks (f) 

3 μg/g body weight 

4× 76 weeks 

(m) 

48/69 

(70%)b 

46/62 

(74%)b 

96 weeks (f) 

Day 42 1.5 μg/g 

body weight 

4× 117 

weeks (m) 135 

9/49 

(18%)b 

1/47 

(2%)b 

weeks (f) 

3 μg/g body weight 

4× 123 

weeks (m) 133 

6/38 

(16%)b 

4/57 

(7%)b 

weeks (f) 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-20

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

DEN Mice liver Control Control Vehicle (0.1 4× 123 8/99 1/97 HighesDiethylnitrosamine (C3AF1) trioctanoin/g weeks (8%) (1%) when d(continued) body weight) (m) ages. 

131weeks (f) Newbo

Day 1 i.p. (3-, 6­

and 6-day intervals) 

1.5 μg/g body weight 

4× 64 weeks 

(m) 84 weeks (f) 

23/32 

(72%)b 

11/39 

(28%)b 

femaletumors incidentreated 

3 μg/g body + higheweight 

4× 59 weeks 

(m) 

39/58 

(67%)b 

26/50 

(52%)b 

76 weeks (f) 

Day 15 1.5 μg/g 

body weight 

4× 82 weeks 

(m) 

22/46 

(48%)b 

8/65 

(12%)b 

102 weeks (f) 

3 μg/g body weight 

4× 74 weeks 

(m) 

35/54 

(65%)b 

22/62 

(35%)b 

94 weeks (f) 

Day 42 1.5 μg/g 

body weight 

4× 105 

weeks (m) 106 

12/56 

(22%)b 

0/53 

(0%)b 

weeks (f) 

3 μg/g body weight 

4× 105 

weeks (m) 103 

9/57 

(16%)b 

0/56 

(0%)b

weeks (f) 

Mice 

(B6C3F1) 

lung Control Control Vehicle (0.1 

trioctanoin/g body weight) 

4× 142 

weeks (m) 137 weeks (f) 

13/98 

(13%) 

9/100 

(9%) 

The minewbotumors animalother tiknown due to emerge
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-21

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

DEN Diethylnitrosamine 

Day 1 i.p. (3-, 6­

and 6-day 

1.5 μg/g body weight 

4× 70 weeks 

(m) 

29/51 

(57%)b 

49/64 

(77%)b 

to their caused 

(continued) intervals) 91 weeks surviva

(f) 

3 μg/g body 

weight 

4× 68 weeks 

(m) 

34/58 

(59%)b 

42/65 

(65%)b 

81 weeks (f) 

Day 15 1.5 μg/g 

body weight 

4× 87 weeks 

(m) 

51/57 

(89%)b 

61/71 

(86%)b 

115 weeks (f) 

3 μg/g body weight 

4× 77 weeks 

(m) 

51/69 

(74%)b 

53/62 

(85%)b 

97 weeks (f) 

Day 42 1.5 μg/g 

body weight 

4× 123 

weeks (m) 129 

38/49 

(78%)b 

38/47 

(81%)b 

weeks (f) 

3 μg/g body weight 

4× 121 

weeks (m) 127 

33/38 

(87%)b 

43/57 

(75%)b

weeks (f) 

Mice 

(C3AF1) 

lung Control Control Vehicle (0.1 

trioctanoin/g 

4× 142 

weeks 

60/99 

(61%) 

50/97 

(52%) 

Of the C3AF1 

body weight) (m) 

137weeks 

lung tuhigher 

(f) multipl

Day 1 i.p. (3-, 6­

and 6-day 

1.5 μg/g body weight 

4× 65 weeks 

(m) 

30/32 

(94%)b 

38/39 

(97%)b 

B6C3F

intervals) 84 weeks 

(f) 

3 μg/g body weight 

4× 59 weeks 

(m) 

49/58 

(84%)b 

46/50 

(92%)b 

76 weeks (f) 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumorsa Dose when Species Target route, Duration of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

DEN Day 15 1.5 μg/g 4× 80 weeks 42/46 61/65 

Diethylnitrosamine body weight (m) (91%)b (94%)b

(continued) 101 

weeks (f) 

3 μg/g body 4× 74 weeks 57/62 

weight 

50/54 

(m) (92%)b 92 weeks 

(93%)b 

(f) 

Day 42 1.5 μg/g 4× 104 52/53 

body weight 

55/56 

weeks (98%)b (98%)b (m) 110 weeks (f) 

3 μg/g body 4× 101 54/56 

weight 

56/57 

weeks (96%)b (98%)b (m) 102 weeks (f) 

Mice liver Control Control None N/A 90 weeks 1/98 0/96 Infant 

(B6C3F1) (1%) (0%) sexes (

more s

Gestation i.p. 1.5 μg/g 1× 2/50 1/51 similarday 18 body weight (4%)b (2%)b adults. 

Day 15 i.p. (3-, 6- 1.5 μg/g 4× 47/51 60/64 

and 6-day body weight (92%)b (94%)b

intervals) Day 42 1.5 μg/g 4× 13/49 3/47 

body weight (26%)b (6%)b 

Day 1 i.p. 1.5 μg/g 1× 73 weeks 15/59 — At the 

body weight (25%)b level, 1

develo

5 μg/g body 1× 29/45 — fewer l

weight (64%)b similar

10 μg/g (Day 1body weight 

1× 24/25 — 

(96%)b 

Tumor 

Day 15 i.p. 1.5 μg/g 1× 13/24 — treated 

body weight (54%)b control

5 μg/g body evaluat

weight 

1× 40/54 — 

(74%)b 

A-22 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumorsa Dose when Species Target route, Duration of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

DEN 10 μg/g 1× 25/25 — 

Diethylnitrosamine body weight (100%)b

(continued)DMBA Rats mammary Day 20 Gavage 10 mg/100 g 1× Week 25 — 3/6 36 of 4

Dimethyl- dosed a

benz[a]anthracene

(Sprague­ adeno­ body weight (50%)b Dawley) sarcoma died so

Day 30 10 mg/100 g 1× Week 26 — 14/15 Highes

body weight (93%)b tumors 

Day 40 in the 4

body weight 

10 mg/100 g 1× Week 27 — 8/9 

with denumbe

(89%)b 

Day 46 10 mg/100 g 1× Week 28 — 8/8 animal

body weight (100%)b 

Day 55 10 mg/100 g 1× Week 29 — 33/34 Anima

body weight 22 wee

treatme

(97%)b 

Day 70 10 mg/100 g 1× Week 32 — 5/8 

body weight (63%)b 

Day 140 10 mg/100 g 1× Week 42 — 10/15 

body weight (67%)b 

Day 180 10 mg/100 g 1× Week 47 — 14/26 

body weight (54%)b

 Control Rats mammary Control None N/A 17 0/22 0/25 Highes

(Wistar) carcinomad 5–8 months (0%) (0%) female

weeks weeks. 

 Control Control None N/A 20 0/31 2/20 Anima

26 weeks months (0%) (10%) for 16 

< Week 2 treatme

56 

Gavage 0.5–1.0 mg 1× Week 40– 0/23 4/50 

(0%)b (8%)b 

Week 5–8 15 mg 1× Week 14– 0/23 14/25 

55 (0%)b (56%)b 

Week 26 15 mg 1× Week 32– 0/34 4/26 

73 (15%)b (0%)b 

Rats (Wistar, mammary Week 5–8 Gavage 15 mg 1× Week 14– 0/21 0/22 

castrated) carcinoma 55 (0%)b (0%)b 

Week 26 15 mg 1× Week 32– 0/33 0/26 

73 (0%)b (0%)b 

A-23 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumorsa Dose when Species Target route, Duration of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

DMBA Rats Total tumors Control Control None N/A 17 0/22 0/25 Total tu

Dimethyl- (Wistar) 5–8 months (0%) (0%) leukembenz[a]anthracene weeks 

(continued) Control Control None N/A 20 2/31 5/20 

26 weeks months (6%) (25%) 

< Week 2 0.5–1.0 mg 1× Week 40– 16/23 36/50 

56 

Gavage 

(70%)b (72%)b 

Week 5–8 15 mg 1× Week 14– 7/23 16/25 

55 (30%)b (64%)b 

Week 26 15 mg 1× Week 32– 12/34 13/26 

73 (50%)b (35%)b 

Mice lung Control: Control Aqueous 1× 40 weeks 0/12 7/23 15 μg D

(BALB/c) Day 1 s.c. gelatine (0%) (30%) to a sig

inciden

Day 1 s.c. 15 μg 1× 40 weeks 14/14 24/24 f tumors 

(100%)b (100%)b admini

Week 2–3 newbo(suckling) 

s.c. 15 μg 1× 42–43 12/23 16/22 

sucklinadults. 

(73%)b weeks (52%)b 

s.c. 30 μg 2× 42–43 14/14 24/24 

(60 μg total) weeks (100%)b (100%)b 

Adulte s.c. 15 μg 1× 48-49 6/12 15/33 

weeks (50%)b (45%)b 

s.c. 30 μg 2× 48-49 9/10 21/23 

(60 μg total) weeks (90%)b (91%)b 

s.c. 30 μg 6× 48-49 12/12 13/13 

(180 μg weeks (100%)b (100%)b 

total) 

 Mice (Swiss) lymphoma Control Control None N/A 31–52 3/408 Higher 

weeks (0.7%) younge

exposu

Day 1 i.p. 30–40 μg 1× 13–33 6/31 

weeks (19%)b Only o

Day 1 group w

weeks 

s.c. 30–40 μg 1× 12–27 8/27 

(30%) others 

b

s.c. inj

Week 8 s.c. 900 μg 1× 30 weeks 1/13 

(8%)b 

A-24 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumorsa Dose when Species Target route, Duration of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

DMBA Mice (Swiss) lung Control Control None N/A 31–52 4/408 

Dimethyl- weeks (0.9%) benz[a]anthracene Day 1 i.p. 30–40 μg 1× 13–33 24/31 (continued) weeks (77%)b 

Day 1 s.c. 30–40 μg 1× 12–27 23/27 

weeks (85%)b 

Week 8 s.c. 900 μg 1× 30 weeks 2/13 

(15%)b 

DMN Rats kidney Day 1 20 mg/kg 1× 1/33 (3)b i.p. ≥5 In the n

Dimethyl- (Wistar) carcinoma months the dos

Day 21 30 mg/kg 1× 5/39 (13)b nitrosamine 20 mg/

Month 1 approx

equiva

30 mg/kg 1× 2/33 (6)b 

Month 1.5 30 mg/kg 1× 1/28 (4)b survivo

Month 2 30 mg/kg 1× 1/26 (4)b 

No con

Month 3 30 mg/kg 1× 10/27 (37)b Month 4 30 mg/kg 1× 7/32 (22)b 

Month 5 30 mg/kg 1× 0/14 (0)b 

Rats kidney Day 1 i.p. 20 mg/kg 1× ≥5 1/33 (3)b 

(Wistar) adenoma months 

Day 21 30 mg/kg 1× 13/39 (33)b Month 1 30 mg/kg 1× 11/33 (33)b 

Month 1.5 30 mg/kg 1× 13/28 (48)b 

Month 2 30 mg/kg 1× 11/26 (42)b Month 3 30 mg/kg 1× 18/27 (67)b Month 4 30 mg/kg 1× 17/32 (53)b Month 5 30 mg/kg 1× 6/14 (43)b 

A-25 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumorsa Dose when Species Target route, Duration of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

DMN Rats kidney Day 1 i.p. 20 mg/kg 1× ≥5 8/33 (24)b Mesen

Dimethyl- (Wistar) mesenchymal months were m

Day 21 30 mg/kg 1× 18/39 (46)b nitrosamine tumors the thre

(continued) groups 

p < 0.0

Month 1 30 mg/kg 1× 23/33 (70)b Month 1.5 30 mg/kg 1× 5/28 (19)b Month 2 30 mg/kg 1× 2/26 (8)b Month 3 30 mg/kg 1× 3/27 (11)b Month 4 30 mg/kg 1× 7/32 (22)b 

Month 5 30 mg/kg 1× 0/14 (0)b 

Rats kidney Day 1 i.p. 20 mg/kg 1× ≥5 2/33 (6)b 

(Wistar) cortical months Day 21 30 mg/kg 1× 16/39 (41)b epithelial 

tumors Month 1 30 mg/kg 1× 12/33 (36)b 

Month 1.5 30 mg/kg 1× 14/28 (52)b Month 2 30 mg/kg 1× 11/26 (42)b Month 3 30 mg/kg 1× 18/27 (67)b Month 4 30 mg/kg 1× 21/32 (66)b

Month 5 30 mg/kg 1× 6/14 (43)b

Rats Total tumors Day 1 i.p. 20 mg/kg 1× ≥5 11/33 (33)b 

(Wistar) months Day 21 30 mg/kg 1× 25/39 (64)b 

Month 1 30 mg/kg 1× 25/33 (76)b Month 1.5 30 mg/kg 1× 17/28 (63)b Month 2 30 mg/kg 1× 13/26 (50)b Month 3 30 mg/kg 1× 18/27 (67)b Month 4 30 mg/kg 1× 22/32 (69)b 

Month 5 30 mg/kg 1× 7/14 (50)b 

A-26 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumorsa Dose when Species Target route, Duration of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

ENU Rats nervous Day 1 Injection 20 mg/kg 1× 100%b Suscep

Ethylnitrosourea system oncoge

Day 30 Injection 20 mg/kg 1× 61%b decline

age. 

Mice liver Control Control None N/A 90 weeks 1/98 0/96 Both m

(B6C3F1) (1%) (0%) mice w

exposu

Gestation i.p. 60 μg/g 1× 28/52 18/49 prenataday 18 body weight (54%)b (37%)b Day 15 60 μg/g 1× 41/50 28/51 

body weight (82%)b (55%)b

Day 42 60 μg/g 1× 10/50 5/50 

body weight (20%)b (10%)b 

Rats nerve tissue Control Control None N/A 4–7 0/16 0/10 Highes

(Wistar) months (0%) (0%) when e

gestatio

Gestation i.p. 40 mg/kg 1× 26/26 18/18 birth. day 16 (100%)b (100%)b

 Day 1 s.c. 40 mg/kg 1× 12/12 16/16 Statisti

(100%)g (100%)g decreas

inciden

 Week 1 40 mg/kg 1× 12/17 18/20 increas

(71%)b (90%)b

exposu

 Week 2 40 mg/kg 1× 10/14 14/18 

(71%)b (78%)b 

 Week 3 40 mg/kg 1× 6/13 5/17 

(46%)b (29%)b

 Week 4 40 mg/kg 1× 8/15 2/10 

(53%)b (20%)b 

A-27 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-28

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration 

of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

ENU Ethylnitrosourea 

Mice (B6C3F1) 

lung Day 1 i.p. 60 μg/g body 

weight 

1× 49/55 

(89%)b 

49/50 

(98%)b 

(continued) Day 15 1× 50/55 

(91%)b 

47/55 

(85%)b 

Day 42 1× 53/59 

(90%)b 

44/51 

(86%)b 

Day 1 120 μg/g body 

weight 

1× 36/38 

(95%)b 

54/60 

(90%)b 

Day 15 1× 45/49 

(92%)b 

43/50 

(86%)b 

Day 42 1× 52/54 

(96%)b 

50/57 

(88%)b 

Mice lung Day 1 60 μg/g body 1× 46/47 51/51 

(C3AF1) weight (98%)g (100%)g 

Day 15 1× 49/49 57/59 

(100%)g (97%)g 

Day 42 1× 59/59 57/57 

(100%)g (100%)g 

Day 1 120 μg/g body 1× 63/64 53/57 

weight (98%)g (93%)g 

Day 15 1× 54/56 50/56 

(96%)g (89%)g

Day 42 1× 59/59 48/48 

(100%)g (100%)g 

Mice liver Day 1 i.p. 60 μg/g body 1× 50/54 28/43 

(B6C3F1) weight (93%)g (65%)g 

Day 15 1× 55/56 33/54 

(98%)g (61%)g 

Day 42 1× 12/40 

(30%)b 

6/39 

(15%)b 

Day 1 120 μg/g body 1× 29/34 32/53 

weight (85%)g (60%)g 

Day 15 1× 45/48 29/43 

(94%)g (67%)g

Day 42 1× 17/49 4/50 

(35%)g (8%)g 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-29

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration 

of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

ENU Mice liver Day 1 i.p. 60 μg/g body 1× 42/45 19/41 Ethylnitrosourea (C3AF1) weight (93%)g (46%)g (continued) Day 15 1× 42/50 

(84%)g 

19/48 

(40%)g 

Day 42 1× 7/29 

(24%)b 

4/50 

(8%)b 

Day 1 120 μg/g body 1× 55/62 19/45 

weight (89%)g (42%)g 

Day 15 1× 35/45 15/35 

(78%)g (43%)g 

Day 42 1× 8/33 

(24%)b 

3/33 

(9%)b 

Mice 

(B6C3F1) 

kidney Day 1 i.p. 60 μg/g body 

weight 

1× 11/48 

(23%)b 

5/49 

(10%)b 

Day 15 1× 6/41 

(15%)b 

7/31 

(23%)b 

Day 42 1× 4/40 

(10%)b 

3/37 

(8%)b 

Day 1 120 μg/g body 

weight 

1× 10/30 

(33%)g 

14/53 

(26%)b 

Day 15 1× 17/37 

(46%)g 

19/49 

(39%)b

Day 42 1× 8/40 

(20%)b 

11/39 

(28%)b 

Mice (C3AF1) 

kidney Day 1 i.p. 60 μg/g body 

weight 

1× 7/44 

(16%)b 

6/45 

(13%)b 

Day 15 1× 7/41 

(17%)b 

8/46 

(17%)b

 Day 42 1× 3/42 

(42%)b 

3/43 

(7%)b

 Day 1 120 μg/g body 

weight 

1× 4/52 

(7%)b 

6/29 

(21%)g

 Day 15 1× 8/35 

(23%)b 

12/29 

(41%)g 

Day 42 1× 6/41 

(71%)b 

3/39 

(8%)b 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-30

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration 

of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

ENU Ethylnitrosourea 

Mice (B6C3F1) 

Harderian Day 1 60 μg/g body 

weight 

1× 7/40 

(17%)b 

5/43 

(12%)b 

(continued) Day 15 1× 10/51 

(20%)b 

17/59 

(29%)b

 Day 42 1× 14/50 

(28%)b 

14/45 

(31%)b

 Day 1 120 μg/g body 

weight 

1× 9/30 

(30%)g 

6/52 

(12%)b

 Day 15 1× 15/41 

(37%)g 

8/31 

(26%)b 

Day 42 1× 25/48 

(52%)g 

14/49 

(29%)b

Mice (C3AF1) 

 Day Harderian 1 60 μg/g body 

weight 

1× 3/25 

(12%)b 

4/35 

(11%)b

 Day 15 1× 1/9 

(11%)b 

6/38 

(16%)b

 Day 42 1× 12/48 

(25%)b 

5/33 

(15%)b

 Day 1 120 μg/g body 

weight 

1× 3/52 

(6%)b 

1/25 

(4%)b

 Day 15 1× 6/46 

(13%)b 

2/52 

(4%)b 

Day 42 1× 5/29 

(17%)b 

2/11 

(18%)b 

Mice (B6C3F1) 

stomach Day 1 60 μg/g body 

weight 

1× 3/48 

(6%)b 

4/43 

(9%)b 

Day 15 1× 10/42 

(24%)g 

7/45 

(16%)b

 Day 42 1× 9/51 

(18%)g 

8/36 

(22%)b

 Day 1 120 μg/g body 

weight 

1× 2/29 

(7%)b 

9/53 

(17%)b

 Day 15 1× 10/35 

(29%)g 

12/33 

(36%)b 

Day 42 1× 12/53 

(23%)g 

12/50 

(24%)b 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-31

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration 

of 

exposure 

Age at 

death 

Tumorsa 

M C

F 

ENU Ethylnitrosourea 

Mice (C3AF1) 

stomach Day 1 60 μg/g body 

weight 

1× 2/39 

(5%)b 

7/45 

(16%)b 

(continued) Day 15 1× 7/45 

(16%)g 

7/38 

(18%)b

 Day 42 1× 14/55 

(25%)g 

7/49 

(14%)b

 Day 1 120 μg/g body 

weight 

1× 8/60 

(13%)b 

9/44 

(20%)b

 Day 15 1× 16/51 

(31%)g 

11/42 

(26%)b 

Day 42 1× 19/48 

(40%)g 

13/37 

(35%)b

Mice (B6C3F1) 

malignant lymphomas 

 Day 1 60 μg/g body 

weight 

1× 2/55 

(4%)b 

6/52 

(12%)g

 Day 15 1× 3/56 

(5%)b 

14/59 

(24%)g

 Day 42 1× 9/59 

(15%)b 

17/59 

(29%)g

 Day 1 120 μg/g body 

weight 

1× 8/39 

(20%)b 

15/65 

(23%)g

 Day 15 1× 14/60 

(23%)b 

17/58 

(29%)g 

Day 42 1× 12/59 

(20%)b 

14/60 

(23%)g 

Mice (C3AF1) 

malignant lymphomas 

Day 1 60 μg/g body 

weight 

1× 6/49 

(12%)b 

8/49 

(16%)g 

Day 15 1× 3/49 

(6%)b 

13/61 

(21%)g

 Day 42 1× 6/60 

(10%)b 

9/55 

(16%)g

 Day 1 120 μg/g body 

weight 

1× 3/66 

(5%)b 

10/58 

(17%)g

 Day 15 1× 10/56 

(18%)b 

18/60 

(30%)g 

Day 42 1× 3/49 

(6%)b 

13/50 

(26%)g 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumor incidencea Dose Duration when Species Target route, of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

NMU Mice Total tumors Control Control N/A N/A 60 weeks 1/20 0% Contro

Methylnitrosourea (BC3F1) (5%) exhibit 

sites ex

lung Day 1 i.p. 50 μg/g body 1× 60 weeks 12/15 16/19 hepato

(84%)b weight (80%)b control 

5 50 μg/g body 1× 60 weeks 10/26 10/35 

weeks weight (39%)b (29%)b 

lympho- Day 1 50 μg/g body 1× 60 weeks 23/39 23/45 

sarcoma (51%)b weight (59%)b 

21/45 

weeks 

5 50 μg/g body 1× 60 weeks 11/35 

weight (31%)b (47%)b 

liver Day 1 50 μg/g body 1× 60 weeks 10/12 1/17 

weight (6%)b (83%)b 

5 50 μg/g body 1× 60 weeks 0%b 0%c weeks weight 

kidney Day 1 50 μg/g body 1× 60 weeks 3/15 3/18 

weight (17%)b (20%)b 

5 50 μg/g body 1× 60 weeks 2/21 0%c weeks weight (10%)b 

fore-stomach Day 1 50 μg/g body 1× 60 weeks 0%b 4/17 

weight (24%)b 

5 50 μg/g body 1× 60 weeks 8/22 12/18 

weeks weight (36%)b (67%)b

 Rats Day 1 i.p. 50 μg/g body 1× 60 weeks 0%b 4/14 

(Wistar) 

mammary Tumor 

weight (29%)b 

on prev

control 

5 50 μg/g body 1× 60 weeks 0%b 3/5 experimweeks weight (60%)b Porta e

lympho- Day 1 50 μg/g body 1× 60 weeks 1/10 0%b was nosarcoma weight (10%)b reporte

5 50 μg/g body 1× 60 weeks 2/8 1/11 

weeks weight (25%)b (9%)b 

kidney (ana- Day 1 50 μg/g body 1× 60 weeks 14/18 9/13 

plastic) weight (78%)b (69%)b 

5 50 μg/g body 1× 60 weeks 2/5 5/12 

weeks weight (40%)b (42%)b 

A-32 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Chemical 

Species 

(strain) 

Target 

site 

Age 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration 

of 

exposure 

Age at 

death 

Tumor incidencea 

M F C

NMU Methylnitrosourea 

kidney 

(adenoma) 

Day 1 50 μg/g body 

weight 

1× 60 weeks 3/14 

(21%)b 

2/6 

(33%)b

(continued) 5 

weeks 

50 μg/g body 

weight 

1× 60 weeks 1⁄4 

(25%)b 

0%b 

forestomach Day 1 50 μg/g body 

weight 

1× 60 weeks 4/14 

(29%)b 

3/6 

(50%)b 

5 50 μg/g body 1× 60 weeks 0%c 0%b weeks weight 

intestine Day 1 50 μg/g body 

weight 

1× 60 weeks 3/10 

(30%)b 

2/2 

(100%)b 

5 weeks 

50 μg/g body 

weight 

1× 60 weeks 2/4 

(50%)b 

0%b 

Mice thymus control i.p. NA NA 120 wks** 0/34 0/25 *Age a

A-33 (C3Hf/Dp) (0%) (0%) thymic 

Day 1 Day 70 

25 μg NMU/g 

body weight 

25 μg NMU/g 

body weight 

1× 1× 

29 ± 8.4 

wks 

120 wks 

(M)*** 

2/16 

(13%)b 

0/20 

(0%)c 

5/25 

(20%)b 

1/20 

(5%)b 

reportesome, bgroups

**Contr

100 wks sacrific

(F) 

Day 1 Day 21 

50 μg NMU/g 

body weight 

50 μg NMU/g 

body weight 

1× 1× 

16.5 ± 0.7 

wks 

24.5 ± 2.5 

wks 

16/24 

(67%)b 

14/44 

(32%)b 

30/44 

(68%)b 

18/38 

(47%)b

***Age 

mice in regardltype. 

Day 70 50 μg NMU/g 

body weight 

1× 31.4 ± 4.4 

wks 

9/30 

(30%)b 

6/41 

(15%)b 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-34

Dose Age at death Tumor incidenc

Species Target Age when route, Duration of 

Chemical (strain) site first dosed # doses Dose exposure M F M F 

NMU Mice extra-thymic control i.p. NA NA 120 120 1/34 2/25 Methylnitrosourea (C3Hf/Dp) lymphoma weeks weeks (3%) (8%(continued) Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

2/16 

(13%)b 

1/25 

(4%)

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

0/20 

(0%)b 

0/20 

(0%)

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

0/24 

(0%)b 

0/44 

(0%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

1/44 

(2%)b 

0/38 

(0%)

Day 70 50 μg NMU/g 

body weight 

1× 110 

weeks 

90 

weeks 

1/30 

(3%)b 

0/41 

(0%)

lung control i.p. NA NA 120 

weeks 

120 

weeks 

4/34 

(12%) 

6/25 

(24%

Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

7/16 

(44%)b 

13/2

(52%

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

12/20 

(60%)b 

8/20 

(40%

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

5/24 

(21%)b 

11/4

(25%

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

23/44 

(52%)b 

15/3

(39%

Day 70 50 μg NMU/g 

body weight 

1× 110 

weeks 

90 

weeks 

18/30 

(60%)b 

24/4

(59%

liver control i.p. NA NA 120 

weeks 

120 

weeks 

13/34 

(38%) 

1/25 

(4%

Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

9/16 

(56%)g 

2/25 

(8%)

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

12/20 

(60%)g 

2/20 

(10%

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

4/24 

(17%)g 

3/44 

(7%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

21/44 

(48%)g 

1/38 

(2.6%
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-35

Dose Age at death Tumor incidenc

Species Target Age when route, Duration of 

Chemical (strain) site first dosed # doses Dose exposure M F M F 

NMU Methylnitrosourea 

Mice (C3Hf/Dp) 

Day 70 50 μg NMU/g 

body weight 

1× 110 

weeks 

90 

weeks 

8/30 

(27%)g 

2/41 

(5%)

(continued) stomach control i.p. NA NA 120 

weeks 

120 

weeks 

0/34 

(0%) 

5/25 

(20%

Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

2/16 

(13%)b 

10/2

(40%

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

3/20 

(15%)b 

7/20 

(35%

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

2/24 

(8%)b 

1/44 

(2%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

19/44 

(43%)b 

9/38 

(24%

Day 70 50 μg NMU/g 

body weight 

1× 110 

weeks 

90 

weeks 

8/30 

(27%)b 

21/4

(51%

kidney control i.p. NA NA 120 

weeks 

120 

weeks 

0/34 

(0%) 

0/25 

(0%

Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

0/16 

(0%)b 

0/25 

(0%)

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

0/20 

(0%)b 

0/20 

(0%)

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

0/24 

(0%)b 

4/44 

(9%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

1/44 

(2%)b 

4/38 

(11%

Day 70 50 μg NMU/g 

body weight 

1× 110 

weeks 

90 

weeks 

5/30 

(17%)b 

7/41 

(17% 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

A-36

Dose Age at death Tumor incidenc

Species Target Age when route, Duration of 

Chemical (strain) site first dosed # doses Dose exposure M F M F 

NMU Mice ovary control i.p. NA NA 120 120 NA 3/25 Methylnitrosourea (C3Hf/Dp) weeks weeks (12%(continued) Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

NA 2/25 

(8%)

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

NA 4/20 

(20%

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

NA 0/44 

(0%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

NA 9/38 

(24%

Day 70 50 μg NMU/g 

body weight 

1× 110 

weeks 

90 

weeks 

NA 16/4

(39%

mammary control i.p. NA NA 120 

weeks 

120 

weeks 

NA 2/25 

(8%

Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

NA 1/25 

(4%)

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

NA 0/20 

(0%)

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

NA 0/44 

(0%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

1/44 

(2%)b 

0/38 

(0%)

Day 70 50 μg NMU/g 

body weight 

110 

weeks 

90 

weeks 

NA 4/41 

(9.8%

uterus or 

vagina 

control i.p. NA NA 120 

weeks 

120 

weeks 

NA 1/25 

(4%

Day 1 25 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

NA 1/25 

(4%)

Day 70 25 μg NMU/g 

body weight 

1× 120 

weeks 

100 

weeks 

NA 6/20 

(30%

Day 1 50 μg NMU/g 

body weight 

1× 70 

weeks 

80 

weeks 

NA 0/44 

(0%)

Day 21 50 μg NMU/g 

body weight 

1× 100 

weeks 

90 

weeks 

NA 1/38 

(3%)

Day 70 50 μg NMU/g 

body weight 

110 

weeks 

90 

weeks 

7/41 

(17%
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Tumorsa Dose Species Target Age when Duration of Age at route, Chemical (strain) site first dosed Dose exposure death Com

# doses M F 

Urethane Mice lung Newborn s.c. 0.18 mg/g 1× 10 weeks 100%b The avera

(SWR) adenoma body weight of tumors 

increased 

11–22 weeks s.c. 0.25 mg/g 1× 23–34 0%b with dose

body weight weeks 

Mice liver Control Control None N/A 493 days 14/97 1/77 

(C3H/f) (m) (14%) (1%) 

553 days 

(f) 

Day 1 i.p. 0.8 mg/g 1× 481 days 18/39 

body weight 

27/30 

(m) (90%)g (46%)g434 days (f) 

8–10 weeks i.p. 1 mg/g body 1× 321 days 6/25 0/32 

weight (0%)c 

-(m) (24%)c 

lung Control Control None N/A 493 days 0/97 0/77 The numb

(m) (0%) (0%) tumors am

553 days controls w

(f) provided. 

Day 1 i.p. 0.8 mg/g 1× 401 days 19/39 

body weight 

14/30 

(m) (48%)g 408 days 

(46%)g 

(f) 

8–10 weeks i.p. 1 mg/g body 1× 506 days 2/25 0/32 

weight (m) (8%)c (0%)c 

-

reticular Control Control None N/A 493 days 2/97 6/77 

tissue (m) (2%) (8%) 

553 days 

(f) 

Day 1 i.p. 0.8 mg/g 1× 285 days 4/30 22/39 

body weight (m) (56%)g 

343 days 

(13%)c 

(f) 

8–10 weeks i.p. 1 mg/g body 1× - 0/25 4/32 

weight 453 days (25%)c (13%)c 

(f) 

A-37 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Tumorsa Dose Species Target Age when Duration of Age at route, Chemical (strain) site first dosed Dose exposure death Com

# doses M F 

Urethane Mice leukemia Control Control None N/A 8–10 1% Highest tu

(continued) (Swiss) months when dos

Day 1 s.c. 2 mg in 0.05 1× 13/60 Exposure 

mL aqueous (22%)b newborns solution followed 

Day 5 leukemia, 

mL aqueous 

4 mg in 0.05 1× 7/39 

at a mean 

solution 

(18%)b 

days. 

Day 40 20 mg in 0.1 1× 2/63 

mL aqueous (3%)b 

solution 

Mice lung Control Control None N/A 9 weeks 0/15 — The propo

(Swiss) animals w

adenomas 

adenoma 2 weeks (0%) 

Control Control None N/A 11 weeks 0/14 — steadily w4 weeks (0%) exposure. 

Control Control None N/A 13 weeks 1/15 — 6 weeks (7%) 

Control Control None N/A 15 weeks 2/15 — 

8 weeks (13%) 

Control Control None N/A 17 weeks 0/15 — 

10 weeks (0%) 

2 weeks i.p. 1 mg/g body 1× 9 weeks 24/24 — 

weight (100%)b 

4 weeks i.p. 1 mg/g body 1× 11 weeks 23/25 — 

weight (92%)b 

6 weeks i.p. 1 mg/g body 1× 13 weeks 22/25 — 

weight (88%)b 

8 weeks i.p. 1 mg/g body 1× 15 weeks 21/25 — 

weight (84%)b 

10 weeks i.p. 1 mg/g body 1× 17 weeks 19/25 — 

weight (76%)b 

A-38 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Chemical 

Species 

(strain) 

Target 

site 

Age when 

first dosed 

Dose 

route, 

# doses Dose 

Duration of 

exposure 

Age at 

death 

Tumorsa 

M F Com

Urethane (continued) 

Mice (Swiss) 

lung adenoma 

3 weeks i.p. 0.25 mg/g 

body weight 

1× 12 weeks 16/19 

(84%)b 

— 

0.5 mg/g body weight 

1× 12 weeks 16/20 

(80%)b 

— 

1 mg/g body weight 

1× 12 weeks 18/20 

(90%)b 

— 

8 weeks i.p. 0.25 mg/g 

body weight 

1× 17 weeks 4/17 

(24%)b 

— 

0.5 mg/g body weight 

1× 17 weeks 15/16 

(94%)b 

— 

1 mg/g body weight 

1× 17 weeks 18/18 

(100%)b 

— 

A-39
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumor incidencea Dose Duration when Species Target route, of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

Urethane Mice liver Control Control N/A N/A 360–720 10/227 4/222 

(continued) (Swiss) days (4.4%) (8.22%) 

Day 1 s.c. 1 mg/g body 1× 180 days 1/20 0/20 

weight (5%)g (0%)c 

Day 1 s.c. 1 mg/g body 1× 240 days 2/17 0/12 

weight (0%)c (12%)g 

Day 1 s.c. 1 mg/g body 1× 300 days 5/18 0/16 

weight (28%)g (0%)c 

Day 1 s.c. 1 mg/g body 1× 360 days 11/20 0/23 

weight (55%)g (0%)c 

Day 1 s.c. 1 mg/g body 1× 420 days 13/15 2/22 

weight (9%)g (87%)g 

Day 1 s.c. 1 mg/g body 1× 480 days 17/23 2/25 

weight (74%)c (8%)c 

Day 5 s.c. 1 mg/g body 1× 420 days 9/13 2/11 

weight (69.2%)b (18.2%)b 

Day 20 s.c. 1 mg/g body 1× 420 days 1/13 0/16 

weight (0%)b (8%)b 

Day 40 s.c. 1 mg/g body 1× 420 days 0/11 0/9 

weight (0%)b (0%)b

 Mice skin Control Control N/A N/A 180–550 30/712 Croton 

(Swiss) days (4.21%) initiate

age. Day 1 s.c. 1 mg single 660 days 26/59 

urethane/g dose (44.1%)g 

body weight; urethane, 

5% croton oil croton oil 

applied 2×/week for 10 mos 

A-40 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumor incidencea Dose Duration when Species Target route, of Age at first Chemical (strain) site # doses Dose exposure death C

dosed M F 

Urethane Day 40 s.c. 1 mg single 700 days 8/41 

(continued) urethane/g dose (19.5%)b 

body weight; urethane, 

5% croton oil croton oil 

applied 2×/week for 10 mos 

Mice liver Control gavage N/A N/A 71 weeks 1/25 0/25 (B6AF1/J) (4%) (0%) 

Day 1 1 mg/g body 1× 66 weeks 9/20 9/26 

weight (45%)g (35%)g 

Day 7 1 mg/g body 1× 67 weeks 20/22 20/26 

weight (77%)g (91%)g 

Day 14 1 mg/g body 1× 68 weeks 16/20 10/23 

weight (80%)g (43%)g 

Day 21 1 mg/g body 1× 69 weeks 13/23 1/20 

weight (57%)g (5%)g 

Day 28 1 mg/g body 1× 70 weeks 4/24 1/20 

weight (17%)g (5%)g 

lung Control gavage 1 mg/g body 1× 71 weeks 9/25 6/25 

weight (36%) (24%) 

Day 1 1 mg/g body 1× 66 weeks 20/20 25/26 

weight (100%)b (96%)b 

Day 7 1 mg/g body 1× 67 weeks 22/22 26/26 

weight (100%)b (100%)b 

Day 14 1 mg/g body 1× 68 weeks 19/20 19/23 

weight (95%)b (83%)b 

Day 21 1 mg/g body 1× 69 weeks 23/23 19/20 

weight (100%)b (95%)b

 Day 28 1 mg/g body 1× 70 weeks 24/24 20/20 

weight (100%)b (100%)b

 Mice Harderian Control gavage 1 mg/g body 1× 71 weeks 0/25 0/25 

(B6AF1/J) gland weight (0%) (0%) 

Day 1 1 mg/g body 1× 66 weeks 0/20 1/26 

weight (0%)c (4%)b 

A-41 
Table 3. Methodological information and tumor incidence for animal studies with early postnatal a

and adult acute exposure (continued) 

Age Tumor incidencea 

Chemical 

Species 

(strain) 

Target 

site 

when 

first 

dosed 

Dose 

route, 

# doses Dose 

Duration 

of 

exposure 

Age at 

death M F C

Urethane (continued) Day 7 1 mg/g body 

weight 

1× 67 weeks 0/22 

(0%)c 

1/26 

(4%)b 

Day 14 1 mg/g body 

weight 

1× 68 weeks 0/20 

(0%)c 

2/23 

(9%)b 

Day 21 1 mg/g body 

weight 

1× 69 weeks 1/23 

(4%)b 

0/20 

(0%)c 

Day 28 1 mg/g body 1× 70 weeks 0/24 0/20 

weight (0%)c (0%)c 

forestomach Control gavage 1 mg/g body 1× 71 weeks 0/25 1/25 

weight (0%) (4%) 

Day 1 1 mg/g body 

weight 

1× 66 weeks 0/20 

(0%)c 

3/26 

(12%)b 

A-42 

Day 7 1 mg/g body 

weight 

1× 67 weeks 1/22 

(5%)b 

1/26 

(4%)b 

Day 14 1 mg/g body 

weight 

1× 68 weeks 1/20 

(5%)b 

4/23 

(17%)b 

Day 21 1 mg/g body 

weight 

1× 69 weeks 0/23 

(0%)c 

1/20 

(5%)b 

Day 28 1 mg/g body 

weight 

1× 70 weeks 2/24 

(8%)b 

1/20 

(5%)b 

a Where not delineated by gender, data combined by study authors or gender not specified. Where percentages only are given, number of b Not evaluated by authors. c Evaluated but not significant compared with controls.

d Study also included mammary fibroadenomas and fibromas as well as other types of cancers. e 8–9 weeks old.

f Includes survivors up to 40 weeks only. g Significant compared with controls. 

i.p. = intraperitoneal injection; s.c. = subcutaneous injection 
Table 4. Ratio of early-life to adult cancer potencies for studies with repeated exposures of juvenile 

animals to carcinogens with a mutagenic mode of action* 

A-43

Unweighted 

Species geometric 

Compound (strain) Sex Dose Tumor mean 2.5% Median 9Benzidine Mice (B6C3F1) male liver 111 64 110 

female liver 0.16 0.004 0.22 

3-MU 3-Methylcholanthrene (formerly known as 20­methylcholanthrene) 

Mice (Albino) male 0.25 mg/g hepatoma 33 7.4 30 

female 0.25 mg/g hepatoma 7.7 1.1 7.1 

male 0.25 mg/g forestomach 0.91 0.39 0.91 

female 0.25 mg/g forestomach 1.5 0.58 1.5 

male 0.25 mg/g skin 1.8 0.048 2.1 

female 0.25 mg/g skin 1.5 0.023 1.8 

Safrole Mice (B6C3F1) male liver 47 16 44 

female liver 0.12 0.002 0.18 

VC Vinyl chloride 

Rats (SpragueDawley) male 6,000 ppm liver-angiosarcoma 6.7 0.035 9.8 

male 10,000 ppm liver-angiosarcoma 7.4 0.035 11 

female 6,000 ppm liver-angiosarcoma 13 4.9 13 female 10,000 ppm liver-angiosarcoma 30 8.7 29 

male 6,000 ppm zymbal gland 0.73 0.0032 1.1 male 10,000 ppm zymbal gland 0.27 0.0022 0.4 

female 6,000 ppm zymbal gland 0.48 0.0027 0.7 female 10,000 ppm zymbal gland 0.15 0.0014 0.19 

male 10,000 ppm leukemia 21 0.026 37 

female 6,000 ppm leukemia 1.3 0.0035 1.7 female 10,000 ppm leukemia 0.29 0.0019 0.35 

male 6,000 ppm nephroblastomas 0.15 0.0014 0.19 male 10,000 ppm nephroblastomas 0.17 0.0015 0.21 

female 6,000 ppm nephroblastomas 0.28 0.0018 0.33 

female 10,000 ppm nephroblastomas 0.24 0.0017 0.29 

male 6,000 ppm angiosarcomasother sites 0.9 0.0033 1.26 male 10,000 ppm angiosarcomas- 0.25 0.0017 0.30 
Table 4. Ratio of early-life to adult cancer potencies for studies with repeated exposures of juvenile 

animals to mutagenic chemicals (continued) 

A-44

Unweighted 

Species geometric 

Compound (strain) Sex Dose Tumor mean 2.5% Median 9

other sites 

VC female 6,000 ppm angiosarcomas- 0.24 0.0017 0.29 Vinyl chloride other sites (continued) female 10,000 ppm angiosarcomasother sites 0.32 0.0019 0.38 

male 6,000 ppm angiomas & 0.72 0.0031 1.0 

fibromas-other 

sites 

male 10,000 ppm angiomas & 1.4 0.0045 2.36 

fibromas-other 

sites 

female 6,000 ppm angiomas & 0.27 0.0018 0.33 

fibromas-other 

sites 

female 10,000 ppm angiomas & 0.52 0.0024 0.63 

fibromas-other 

sites 

male 6,000 ppm hepatoma 62 11 58 

male 10,000 ppm hepatoma 34 8.2 32 

female 6,000 ppm hepatoma 55 13 51 female 10,000 ppm hepatoma 55 8.4 53 

male 6,000 ppm skin carcinomas 1.1 0.0035 1.5 male 10,000 ppm skin carcinomas 0.41 0.0024 0.56 

female 6,000 ppm skin carcinomas 0.46 0.0024 0.59 female 10,000 ppm skin carcinomas 0.31 0.0019 0.37 

male 6,000 ppm neuroblastoma 0.21 0.0016 0.26 male 10,000 ppm neuroblastoma 0.20 0.0016 0.24 

female 6,000 ppm neuroblastoma 0.27 0.0018 0.32 female 10,000 ppm neuroblastoma 0.14 0.0014 0.18 

* The 2.5% and 97.5% are percentiles of the posterior distribution. For a Bayesian distribution, these perce

manner similar to the 95% confidence limits for other types of statistical analyses. 
Table 5. Ratio of early-life to adult cancer potencies for studies with repeated exposures of juvenile and ad

to chemicals with a nonmutagenic mode of action* 

A-45

Ratio of juvenile to adult potency 

Unweighted 

Species geometric 

Compound (strain) Sex Dose Tumor mean 2.5% Median 97.5% Amitrole Mice (B6C3F1) male NA liver 13 5.1 14 30 

female NA liver 0.14 0.0013 0.18 3.9 

DDT Mice (B6C3F1) male NA liver 1.3 0.0044 2.5 25 Dieldrin Mice (B6C3F1) male NA liver 0.75 0.0031 1.2 27 DPH Rats (F344/N) male 630 liver 0.4 0.0024 0.54 16 

female 630 liver 0.24 0.0017 0.29 12 

 Mice (B6C3F1) male 210 liver 1.5 0.0040 2.4 71 

female 210 liver 1.3 0.0056 2.6 15 

ETU Rats (F344/N) male 90 thyroid 0.37 0.0029 0.61 5.4 

female 90 thyroid 0.23 0.0018 0.3 7.0 

 Mice (B6C3F1) male 330 liver 0.091 0.0011 0.12 1.9 

female 330 liver 0.057 0.0010 0.081 0.65 

male 330 thyroid 0.41 0.0022 0.52 25 

female 330 thyroid 0.4 0.0024 0.55 16 

male 330 pituitary 0.32 0.0019 0.38 22 

female 330 pituitary 0.24 0.0018 0.32 6.9 

PBB Rats (F344/N) male 10 liver 0.59 0.0041 1.1 6.6 

female 10 liver 0.063 0.0009 0.079 1.2 

male 10 mononuclear 

cell leukemia 

0.79 0.0035 1.4 18 

female 10 mononuclear 

cell leukemia 

0.21 0.0017 0.28 6.0 

 Mice (B6C3F1) male 30 liver 3.9 1.9 3.9 7.5 

female 30 liver 1.0 0.37 1.05 2.1 

* The 2.5% and 97.5% are percentiles of the posterior distribution. For a Bayesian distribution, these perce

manner similar to the 95% confidence limits for other types of statistical analyses. 
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles and adul

carcinogens with a mutagenic mode of action* 

A-46

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

BaP* Mice (B6C3F1) male 75 μg/kg liver 1 day 9.3 2.9 8.4 5

 15 days 11 3.5 9.6 6

female 75 μg/kg 1 day 1.2 0.0083 1.6 3

 15 days 1.7 0.015 2.1 3

male 150 μg/kg 1 day 29 8.2 26 19

 15 days 15 4.1 13 10

female 150 μg/kg 1 day 8.8 1.4 8.1 9

 15 days 1.2 0.0082 1.6 3

Mice (C3AF1) male 75 μg/kg liver 1 day 11 2.1 10 11

 15 days 7.5 1.1 7.0 8

female 75 μg/kg 1 day 0.2 0.0018 0.26 9.

 15 days 0.2 0.0017 0.24 8.

male 150 μg/kg 1 day 14 3.0 12.8 13

 15 days 3.6 0.11 3.8 4

female 150 μg/kg 1 day 0.2 0.0017 0.24 8.

 15 days 0.2 0.0017 0.24 8.

 Mice (B6C3F1) Male 75 μg/kg lung 1 day 1.2 0.45 1.2 3.

15 days 0.2 0.0046 0.31 1.

female 75 μg/kg lung 1 day 2.8 1.096 2.7 9.

15 days 1.4 0.41 1.4 5.

Male 150 μg/kg lung 1 day 2.2 1.0 2.1 5.

15 days 0.8 0.2 0.82 2.

female 150 μg/kg lung 1 day 7.9 2.6 7.2 4

15 days 3.7 1.1 3.4 2

 Mice (C3AF1) male 75 μg/kg lung 1 day 1.2 0.47 1.2 3.

15 days 1.1 0.43 1.08 3.
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-47

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

BaP* (continued) 

female 75 μg/kg lung 1 day 1.6 0.66 1.55 4.

15 days 1.6 0.71 1.63 4.

male 150 μg/kg lung 1 day 1.5 0.57 1.5 5.

15 days 1.9 0.71 1.8 6.

female 150 μg/kg lung 1 day 1.3 0.61 1.3 2.

15 days 1.2 0.54 1.1 2.

DBA Mice lung 178 20 143 51DEN** Mice (B6C3F1) male 6 μg/kg liver 1 day 9.0 3.5 8.3 3

15 days 8.9 3.5 8.2 3

female 6 μg/kg liver 1 day 35 9.1 31 23

15 days 25 6.3 226 17

male 12 μg/kg liver 1 day 9.6 3.3 8.8 5

15 days 9.8 3.4 8.9 5

female 12 μg/kg liver 1 day 16 5.9 15 6

15 days 19 7.1 18 7

 Mice (C3AF1) male 6 μg/kg liver 1 day 7.3 2.9 6.9 2

15 days 3.5 1.4 3.3 1

female 6 μg/kg liver 1 day 17 3.2 16 16

15 days 6.4 0.86 6.0 7

male 12 μg/kg liver 1 day 11 3.7 9.5 5

15 days 9.8 3.4 8.9 5

female 12 μg/kg liver 1 day 40 8.5 36 34

15 days 25 5.0 22 22

 Mice (B6C3F1) male 6 μg/kg lung 1 day 0.5 0.27 0.52 0.9

15 days 1.6 0.95 1.6 2.

female 6 μg/kg lung 1 day 0.9 0.54 0.89 1.

15 days 1.2 0.76 1.2 2.
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-48

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

DEN** (continued) 

male 12 μg/kg lung 1 day 0.4 0.21 0.40 0.7

15 days 0.7 0.39 0.66 1.

female 12 μg/kg lung 1 day 0.7 0.44 0.73 1.

15 days 1.4 0.88 1.4 2.

 Mice (C3AF1) male 6 μg/kg lung 1 day 0.7 0.22 0.67 1.

15 days 0.5 0.21 0.56 1.

female 6 μg/kg lung 1 day 1.1 0.45 1.1 2.

15 days 0.7 0.36 0.74 1.

male 12 μg/kg lung 1 day 0.3 0.084 0.33 0.7

15 days 0.6 0.26 0.62 1.

female 12 μg/kg lung 1 day 0.7 0.35 0.75 1.

15 days 0.7 0.37 0.75 1.

DMBA# Rats (Wistar) male total 2 vs 5–8 wks 3.3 1.3 3.2 1

2 vs 26 wks 3.2 1.3 3.1 9.

female total 2 vs 5–8 wks 1.3 0.68 1.3 2.

2 vs 26 wks 3.3 1.2 3.0 1

mammary 2 vs 5–8 wks 0.0 0.0012 0.056 0.2

2 vs 26 wks 0.2 0.0023 0.29 5.5 vs 26 wks 7.1 1.8 6.4 5

Mice (Balb/c) male 15 μg lung 1 day 30 2.8 22 14

15–19 days 1.0 0.28 1.0 3.

male 30 μgx2 lung 15–19 days 14 1.056 10 97

female 15 μg lung 1 day 60 6.0 46 23

15–19 days 3.1 0.51 3.0 2

female 30 μgx2 lung 15–19 days 15 1.2 11 10

Mice (Swiss) lymphoma 2.7 0.60 2.5 1

lung 9.1 2.9 8.7 4
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-49

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

%

DMN*** Rats (Wistar) 3 wks total 1 month 0.7 0.41 0.73 1.

1.5 months 1.1 0.58 1.1 2.

2 months 1.5 0.75 1.5 3.3 months 0.9 0.50 0.94 1.

24 hr 1 month 0.3 0.13 0.28 0.

1.5 months 0.4 0.18 0.42 0.

2 months 0.6 0.24 0.56 1.3 months 0.4 0.16 0.36 0.7

1 month 1.5 months 1.5 0.80 1.52 3.

2 months 2.0 1.0 2.0 4.3 months 1.3 0.69 1.3 2.

ENU Mice (B6C3F1) male liver 7.8 3.9 7.7 1

female 7.1 2.9 6.9 2

Rats (Wistar) male nerve tissue 1 day 27 2.5 20 13

1 week 1.6 0.61 1.6 4.

2 weeks 1.6 0.58 1.6 4.3 weeks 0.7 0.12 0.72 2.

female 1 day 64 6.0 50 24

1 weeks 9.6 2.6 8.9 52 weeks 6.2 1.6 5.7 43 weeks 0.7 0.0090 0.89 8.

Mice (B6C3F1) male 60 μg/g lung 1 1.0 0.60 1.0 1.

15 1.1 0.66 1.1 1.

female 60 μg/g lung 1 2.1 1.17 2.1 4.

15 1.0 0.60 1.0 1.

male 120 μg/g lung 1 1.0 0.60 1.0 1.
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-50

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

15 1.1 0.66 1.0 1.

ENU (continued) 

female 120 μg/g lung 1 2.1 1.2 2.1 4.

15 1.0 0.60 1.0 1.

 Mice (C3AF1) male 60 μg/g lung 1 8.7 2.7 8.0 4

15 52 5.2 39 21

female 60 μg/g lung 15 0.7 0.32 0.72 1.

male 120 μg/g lung 1 0.9 0.38 0.92 2.

15 0.7 0.28 0.67 1.

female 120 μg/g lung 1 0.5 0.24 0.54 1.

15 0.4 0.18 0.42 0.9

 Mice (B6C3F1) male 60 μg/g liver 1 8.8 4.2 8.5 2

15 14 6.2 14 3

female 60 μg/g liver 1 6.3 2.6 6.1 1

15 5.6 2.4 5.4 1

male 120 μg/g liver 1 5.2 2.5 5.1 1

15 7.6 3.9 7.5 1

female 120 μg/g liver 1 11 4.1 11 4

15 14 4.9 13 5

 Mice (C3AF1) male 60 μg/g liver 1 12 4.7 11 4

15 8.1 3.2 7.6 2

female 60 μg/g liver 1 7.5 2.6 7.0 3

15 4.8 1.8 4.6 1

male 120 μg/g liver 1 9.8 4.1 9.3 3

15 6.6 2.7 6.3 2

female 120 μg/g liver 1 5.4 1.7 5.0 2

15 5.4 1.7 5.1 2

 Mice (B6C3F1) male 60 μg/g kidney 1 2.2 0.73 2.1 8.

15 1.2 0.29 1.2 5.
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-51

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

female 60 μg/g kidney 1 0.7 0.024 0.85 5.

15 2.6 0.61 2.5 1

ENU (continued) 

male 120 μg/g kidney 1 1.7 0.65 1.7 4.

15 2.6 1.14 2.6 6.

female 120 μg/g kidney 1 0.9 0.37 0.87 2.

15 1.4 0.67 1.4 3.

 Mice (C3AF1) male 60 μg/g kidney 1 1.8 0.17 1.9 1

15 2.0 0.25 2.0 1

female 60 μg/g kidney 1 1.0 0.016 1.3 1

15 2.1 0.16 2.2 2

male 120 μg/g kidney 1 0.2 0.0029 0.24 1.

15 1.5 0.38 1.5 5.

female 120 μg/g kidney 1 2.3 0.17 2.4 2

15 7.1 1.8 6.5 4

 Mice (B6C3F1) male 60 μg/g Harderian 1 0.3 0.018 0.41 1.

15 0.5 0.075 0.52 1.

female 60 μg/g Harderian 1 0.1 0.0025 0.16 0.7

15 0.8 0.35 0.84 2.

male 120 μg/g Harderian 1 0.4 0.13 0.42 0.9

15 0.6 0.26 0.57 1.

female 120 μg/g Harderian 1 0.1 0.0030 0.18 0.8

15 0.7 0.17 0.77 2.

 Mice (C3AF1) male 60 μg/g Harderian 1 0.1 0.0023 0.20 1.

15 0.1 0.0016 0.18 1.

female 60 μg/g Harderian 1 0.4 0.019 0.52 2.

15 0.8 0.15 0.85 3.

male 120 μg/g Harderian 1 0.1 0.0010 0.086 1.

15 0.3 0.0050 0.40 2.
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-52

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

female 120 μg/g Harderian 1 0.1 0.0012 0.094 1.

15 0.1 0.0012 0.081 0.9

ENU (continued) 

Mice (B6C3F1) male 60 μg/g stomach 1 0.3 0.0091 0.34 2.

15 1.9 0.61 1.82 8.

female 60 μg/g stomach 1 0.2 0.0083 0.26 1.

15 0.2 0.0072 0.24 1.

male 120 μg/g stomach 1 0.2 0.0059 0.20 0.9

15 1.2 0.50 1.2 2.

female 120 μg/g stomach 1 0.6 0.19 0.60 1.

15 1.6 0.67 1.6 3.

 Mice (C3AF1) male 60 μg/g stomach 1 0.0 0.0009 0.063 0.5

15 0.3 0.023 0.41 1.

female 60 μg/g stomach 1 0.8 0.085 0.89 3.

15 1.1 0.19 1.1 4.

male 120 μg/g stomach 1 0.2 0.010 0.19 0.5

15 0.7 0.32 0.70 1.

female 120 μg/g stomach 1 0.4 0.14 0.46 1.

15 0.6 0.24 0.64 1.

NMU Mice (BC3F1) male 50 μg/g lung adenomas 1 3.4 1.3 3.3 9.

female 50 μg/g lung adenomas 1 6.3 2.4 6.0 2

male 50 μg/g lymphosarcoma 1 2.5 1.1 2.4 6.

female 50 μg/g lymphosarcoma 1 1.1 0.49 1.1 2.

male 50 μg/g hepatoma 1 35 6.5 32 32

female 50 μg/g hepatoma 1 0.3 0.0023 0.39 1

male 50 μg/g renal adenoma 1 0.9 0.0093 1.2 1

female 50 μg/g renal adenoma 1 1.3 0.0081 1.7 3

male 50 μg/g forestomach 1 0.0 0.0006 0.039 0.5

female 50 μg/g forestomach 1 0.1 0.0027 0.15 0.6
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-53

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

Mice (C3Hf/Dp) male 25 μg/g thymic 

lymphoma 

1 1.9 0.048 2.1 2

NMU (continued) 

 female 25 μg/g thymic 

lymphoma 

1 1.2 0.0089 1.5 3

male 25 μg/g lung adenomas 1 1.0 0.013 1.2 1

female 25 μg/g lung adenomas 1 0.4 0.018 0.46 1. 

male 25 μg/g liver tumor 1 0.2 0.0016 0.21 4.

female 25 μg/g liver tumor 1 0.3 0.0026 0.39 4.

male 25 μg/g Stomach 1 0.5 0.0045 0.67 6.

female 25 μg/g Stomach 1 0.3 0.0046 0.43 3.

ovarian 1 0.1 0.0014 0.17 3.

uterine/vaginal 1 8.6 1.1 8.1 9

male 50 μg/g thymic 

lymphoma 

1 7.9 3.1 7.4 3

female 50 μg/g thymic 

lymphoma 

1 3.1 1.3 3.0 7.

male 50 μg/g lung adenomas 1 0.04 0.0008 0.058 0.4

female 50 μg/g lung adenomas 1 0.1 0.0012 0.084 0.5

male 50 μg/g liver tumor 1 0.2 0.0021 0.33 7.

female 50 μg/g liver tumor 1 0.1 0.0011 0.13 4.

male 50 μg/g Stomach 1 0.01 0.0003 0.013 0.1

female 50 μg/g Stomach 1 0.1 0.0022 0.15 0.9

ovarian 1 0.0 0.0003 0.014 0.1

uterine/vaginal 1 0.0 0.0005 0.034 0.4

male 50 μg/g thymic 

lymphoma 

21 4.3 1. 6 4.1 1

female 50 μg/g thymic 

lymphoma 

21 1.0 0.39 1.0 2.

male 50 μg/g lung adenomas 21 0.1 0.0022 0.22 1.

female 50 μg/g lung adenomas 21 0.7 0.30 0.75 1.
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

Ratio of juvenile to adult potency 

Unweighted 

Compound 

Species 

(strain) Sex Dose Tumor Day geometric mean 2.5% Median 97

% 

male 50 μg/g liver tumor 21 0.1 0.0013 0.15 4.

female 50 μg/g liver tumor 21 0.9 0.0051 1.4 2

NMU male 50 μg/g stomach 21 0.1 0.001 0.08 0.6(continued) female 50 μg/g stomach 21 1.8 0.77 1.8 4.

ovarian 21 0.0 0.0007 0.055 0.9

uterine/vaginal 21 1.7 0.59 1.7 6.

Urethane Mice (Swiss) male 1 mg/g liver 1 24 4.4 21 22

female 1 mg/g liver 1 0.4 0.0044 0.54 1

male 1 mg/g liver 5 14 2.4 13 13

female 1 mg/g liver 5 1.2 0.017 1.4 2

A-54 male 1 mg/g liver 20 0.2 0.0018 0.28 1

female 1 mg/g liver 20 0.1 0.0011 0.12 4.

both 1 mg/g skin 1 0.2 0.0027 0.32 5.

Urethane + Mice (Swiss) both 1 mg/g skin 1 2.9 1.2 2.8 8.croton oil Urethane Rats (MRC male/ 16%×6 neurilemmomas 1 0.2 0.0028 0.33 4.

Wistar-derived) female 

male/ 16%×6 neurilemmomas 28 0.4 0.0045 0.51 6.

female 

male/ 16%×6 liver 1 7.9 1.4 7.1 8

female 

male/ 16%×6 liver 28 0.2 0.0026 0.4 11

female 

male/ 16%×6 thyroid 1 0.0 0.0006 0.039 0.6

female 

male/ 16%×6 thyroid 28 0.1 0.0011 0.1 1.

female 

 Mice (Swiss) male/ 1 mg/g lung 1 15 1.2 11 99

female 

 Mice (Swiss) leukemia 6.7 1.7 6.1 4
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-55

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

5.1 1.1 4.7 3

Urethane (continued) 

Mice (B6AF1/J) male 1 mg/g liver 21 5.1 1.4 4.7 3

female 1 mg/g liver 21 0.2 0.0019 0.26 6.

Harderian gland 1 0.3 0.0021 0.33 1

7 0.3 0.0021 0.33 1

14 0.6 0.0044 0.85 2

male 1 mg/g Harderian gland 21 0.3 0.0024 0.41 1

male 1 mg/g forestomach 1 0.1 0.0009 0.079 1.

female 1 mg/g forestomach 1 0.4 0.0028 0.49 1

male 1 mg/g forestomach 7 0.1 0.0017 0.19 3.

female 1 mg/g forestomach 7 0.1 0.0013 0.16 5.

male 1 mg/g forestomach 14 0.2 0.0018 0.21 3.

female 1 mg/g forestomach 14 0.8 0.0056 1.1 1

male 1 mg/g forestomach 21 0.1 0.0008 0.072 1.

female 1 mg/g forestomach 21 0.2 0.0015 0.2 6.

lung 1 1.0 0.36 0.95 2.

male 1 mg/g lung 14 0.8 0.26 0.8 2.

female 1 mg/g lung 14 0.4 0.16 0.45 1.

21 0.9 0.31 0.86 2.

Mice (C3H/f) male 1 mg/g liver 1 14 4.0 12 8

female 1 mg/g liver 1 16 3.2 15 15

male 1 mg/g lung 1 5.9 1.7 5.6 2

female 1 mg/g lung 1 22 4.5 20 20

male 1 mg/g reticular tissue 1 2.0 0.023 2.3 3

female 1 mg/g reticular tissue 1 8.6 2.3 7.7 6

Mice (Swiss) 1 mg/g pulmonary 

adenomas 

2 vs 4 weeks 14 1.1 10.1 96
Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles a

animals to carcinogens with a mutagenic mode of action (continued) 

A-56

Compound 

Species 

(strain) Sex Dose Tumor Day 

Ratio of juvenile to adult potency 

Unweighted 

geometric 

mean 2.5% Median 

97

% 

1 mg/g pulmonary 

adenomas 

2 vs 6 weeks 16 1.3 11.3 10

Urethane (continued) 

1 mg/g pulmonary 

adenomas 

2 vs 8 weeks 19 1.6 13.3 11

1 mg/g pulmonary 

adenomas 

2 vs 10 weeks 21 1.9 14.5 11

0.25 mg/g adenomas 3 vs 8 weeks 7.1 2.3 6.7 2

0.5 mg/g adenomas 3 vs 8 weeks 0.7 0.29 0.67 1.1.0 mg/g adenomas 3 vs 8 weeks 0.7 0.28 0.68 1.

* The 2.5% and 97.5% are percentiles of the posterior distribution. For a Bayesian distribution, these perce

manner similar to the 95% confidence limits for other types of statistical analyses. 
Table 7. Ratio of early-life to adult cancer potencies for studies with lifetime exposures starting wit

and adult animals to carcinogens with mutagenic or nonmutagenic modes of action* 

A-57

Unweightedg 

Species eometric 

Compound (strain) Sex Dose Tumor mean 2.5% Median 97.5% Mutagenic compounds DEN Rats (Colworth) multiple liver 2.8 0.0093 5.6 23 

esophagus 0.18 0.0015 0.23 4.8 

Safrole Mice (B6C3F1) male liver 50 3.7 50 253 

female liver 4.0 0.007 4.0 23 

Urethane Mice (B6AF1/J) male 2.5 mg/pup liver 79 0.36 102 1,064 

female 2.5 mg/pup liver 0.47 0.0022 0.55 42 

Nonmutagenic compounds DDT Mice (B6C3F1) liver 23 0.0023 0.58 23 Dieldrin Mice (B6C3F1) liver 91 0.014 14 91 DPH Rats (F344/N) male 630:800 liver 0.31 0.0019 0.37 18 

630:2,400 liver 0.36 0.0021 0.45 17 

female 630:800 liver 0.33 0.0019 0.39 21 

630:2,400 liver 0.33 0.0019 0.39 21 

 Mice (B6C3F1) male 210:100 liver 0.71 0.0028 0.93 49 

210:300 liver 14 0.03 23 214 

female 210:200 liver 0.32 0.002 0.42 13 

210:600 liver 0.35 0.0023 0.53 8.8 

ETU Rats (F344/N) male 90:83 thyroid 0.23 0.0017 0.3 7.3 

90:250 thyroid 9.1 1.1 10.5 27 

female 90:83 thyroid 0.37 0.0021 0.46 19 

90:250 thyroid 0.61 0.0034 1.1 10 
Table 7. Ratio of early-life to adult cancer potencies for studies with lifetime exposures starting wit

and adult animals to carcinogens with mutagenic or nonmutagenic modes of action (continued) 

A-58

Unweighted 

Species geometric 

Compound (strain) Sex Dose Tumor mean 2.5% Median 97.5% ETU (continued) 

Mice (B6C3F1) male 330:330 liver 0.37 0.0022 0.5 14 

330:1,000 liver 0.48 0.0027 0.75 12 

female 330:330 liver 0.33 0.0023 0.5 7.8 

330:1,000 liver 0.42 0.0025 0.65 11 

male 330:330 thyroid 0.44 0.0022 0.52 34 

330:1,000 thyroid 0.63 0.0035 1.12 10 

female 330:330 thyroid 5.2 0.011 10 108 

330:1,000 thyroid 0.18 0.0016 0.24 4.2 

male 330:330 pituitary 0.40 0.0021 0.47 32 

330:1,000 pituitary 0.18 0.0015 0.22 5.7 

female 330:330 pituitary 0.21 0.0016 0.26 10 

330:1,000 pituitary 0.27 0.0019 0.36 9.0 

PBB Rats (F344/N) male 10:10 liver 0.39 0.0023 0.56 13 

10:30 liver 0.18 0.0016 0.25 4.3 

female 10:10 liver 36 15 36 86 

10:30 liver 3.1 0.023 4.6 22 

male 10:10 mononuclear cell 

leukemia 

0.51 0.0025 0.69 23 

male 10:30 mononuclear cell 

leukemia 

0.77 0.0031 1.1 35 

female 10:10 mononuclear cell 

leukemia 

0.54 0.0026 0.74 24 

female 10:30 mononuclear cell 

leukemia 

0.34 0.0021 0.45 15 

 Mice (B6C3F1) male 30:30 liver 8.9 0.015 12.2 1,076 

female 30:30 liver 4.4 0.0075 6.2 786 

male 10:10 liver 0.15 0.0014 0.2 3.9 
Table 7. Ratio of early-life to adult cancer potencies for studies with lifetime exposures starting wit

and adult animals to carcinogens with mutagenic or nonmutagenic modes of action (continued) 

Compound 

Species 

(strain) Sex Dose Tumor 

Unweighted 

geometric 

mean 2.5% Median 97.5% 

female 10:10 liver 0.29 0.0021 0.43 7.0 

* The 2.5% and 97.5% are percentiles of the posterior distribution. For a Bayesian distribution, these perce

manner similar to the 95% confidence limits for other types of statistical analyses. 

A-59
Table 8. Summary of quantitative estimates of ratio of early-life to adult cancer potencies 

A-60

InverseDose Tissue Number of chemicals weighted geometric mean ratio Unweighted Minimum Unweighted Maximum Number 

ratios 

Chemicals with mutagenic mode of action Repeated 4 10.5 0.12 111 45 Lifetime 3 8.7 0.18 79 6 

Combined repeated and lifetime 6 10.4 0.12 111 51 

Acute Combined 11 1.5 0.01 178 268 

 Forestomach 3 0.076 0.01 1.9 32  Harderian 2 0.48 0.06 0.8 20  Kidney 2 1.6 0.17 7.1 18  Leukemia 1 5.9 5.1 6.7 2  Liver 5 8.1 0.10 40 70  Lung 7 1.1 0.04 178 77  Lymph 2 1.8 1.1 2.7 3 

Mammary (wk 5 vs wk 26) 1 7.1 NA NA 1 

Mammary (wk 2 vs wk 5–8 or 26) 1 0.071 NA NA 2 

 Nerve 2 2.3 0.24 64 8 

Nerve (Day 1 comparison) 2 10 0.24 64 3 

 Ovarian 1 0.033 0.01 0.13 3  Reticular tissue 1 6.5 1.96 8.6 2  Thymic lymphoma 1 2.8 1.01 7.9 6  Thyroid 1 0.05 0.03 0.08 2  Uterine/vaginal 1 1.6 0.03 8.6 3  Day 1 7 1.7 0.01 178 127  Day 15 3 1.5 0.06 52 74 

Chemicals with nonmutagenic mode of action Repeated 6 2.2 0.06 13 22 Lifetime 5 3.4 0.15 36 38 
Table 9. Excess Relative Risk (ERR) estimates for cancer incidence from 

Life Span Study (Japanese survivors)a 

Average ERR at 1 Sv 

Site <20b

 >20b 

Stomach 0.74 0.24 

Colon 0.62 0.7 

Liver 1.3 0.31 

Lung 0.57 1.1 

Bone and connective tissue 11 0.42 

Skin 5.4 0.39 

Breast 3.3 0.98 

Urinary bladder 0.71 0.79 

Leukemia 6.1 3.7 a

 Information extracted from tables in UNSCEAR, Annex I (2000). 

b Age at exposure. 

A-61
Table 10. Excess Relative Risk (ERR) estimates for incidence of thyroid 

cancer from Life Span Studya 

Age at exposure 

Average ERR at 1 Sv 

(No. cases) 

0–9 yr 10.25 (24) 

10–19 yr 4.5 (35) 

20–29 yr 0.10 (18) 

>30 yr 0.04 (55) a Information extracted from tables in UNSCEAR, Annex I (2000). 

A-62 
Table 11. Coefficients for the Revised Methodology mortality risk model 

(from U.S. EPA, 1999)a 

Cancer type b 

40+ 

R 

R 

R 

R 

A 

A 

R 

R 

R 

R 

A 

R 

Female: 

R 

R 

R 

R 

A 

A 

R 

R 

R 

R 

A 

R 

Risk model Age group 

type 0–9 10–19 20–29 30–39 

Male: 

Stomach 1.223 1.972 2.044 0.3024 0.2745 

Colon 2.290 2.290 0.2787 0.4395 0.08881 

Liver 0.9877 0.9877 0.9877 0.9877 0.9877 

Lung 0.4480 0.4480 0.0435 0.1315 0.1680 

Bone 0.09387 0.09387 0.09387 0.09387 0.09387 

Skin 0.06597 0.06597 0.06597 0.06597 0.06597 

Breast 0.0 0.0 0.0 0.0 0.0 

Ovary 0.0 0.0 0.0 0.0 0.0 

Bladder 1.037 1.037 1.037 1.037 1.037 

Kidney 0.2938 0.2938 0.2938 0.2938 0.2938 

Thyroid 0.1667 0.1667 0.1667 0.1667 0.1667 

Leukemia 982.3 311.3 416.6 264.4 143.6 

Stomach 3.581 4.585 4.552 0.6309 0.5424 

Colon 3.265 3.265 0.6183 0.8921 0.1921 

Liver 0.9877 0.9877 0.9877 0.9877 0.9877 

Lung 1.359 1.359 0.1620 0.4396 0.6047 

Bone 0.09387 0.09387 0.09387 0.09387 0.09387 

Skin 0.06597 0.06597 0.06597 0.06597 0.06597 

Breast 0.7000 0.7000 0.3000 0.3000 0.1000 

Ovary 0.7185 0.7185 0.7185 0.7185 0.7185 

Bladder 1.049 1.049 1.049 1.049 1.049 

Kidney 0.2938 0.2938 0.2938 0.2938 0.2938 

Thyroid 0.3333 0.3333 0.1667 0.1667 0.1667 

Leukemia 1,176 284.9 370.06 178.8 157.1 

a The coefficients were derived using several models applied to data from A-bomb survivors and selected medical 

exposures. 

b A = absolute risk with coefficient units of 10-4 (Gy y)-1; R= relative risk with coefficient units of Gy-1. 

A-63 
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