# 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 Technica l Panel of the Risk Assessm ent Forum.

AUTHORS

Hugh Barton, National Health and Environmen tal Effects Research Laboratory, ORD

Jim Cogliano, National Center for Environm ental 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 Envi ronmental Effects Research Laboratory,

ORD

Larry Valcov ic, National Center fo r 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

i i i

# 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, a nd 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 pullin g together the underlying information.

i v

# CONTENTS

PREFACE.......................................................................................................................................v i

1. I NTRODUCTION 

# .............................................................................................................................. 1

2. P ROCEDURES



# ............................................................................................................................... .. 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. R ESULTS



# ............................................................................................................................... ....... 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 Re peated Dosing Studi es 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. D ISCUSSION



# ............................................................................................................................... .. 23

5. G UIDANCE FOR ASSESSING CANCER RISKS FROM EARLY



# - LIFE EXPOSURE 

# .................................... 30

6. C OMBINING 

# L IFESTAGE 

# D IFFERENCES IN 

# E XPOSURE AND 

# D OSE 

# -R ESPONSE 

# W HEN 

# A SSESSING



# C ARCINOGEN 

# R ISK 

# - S OME 

# E XAMPLES FOR 

# C ARCINOGENS 

# T HAT 

# A CT 

# T HROUGH A 

# M UTAGENIC



# M ODE OF ACTION 

# ........................................................................................................................ 36

6.1 C ALCULATING 

# L IFETIME 

# R ISKS 

# A SSOCIATED WITH 

# L IFETIME 

# E XPOSURES 

# ........................... 36

6.2 C ALCULATING 

# L IFETIME 

# R ISKS 

# A SSOCIATED WITH 

# L ESS THAN 

# L IFETIME 

# E XPOSURES 

# ....... 368

A PPENDIX 

# A: T ABLES 

# ................................................................................................................... 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 an alysis. (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 adu lt 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 studie s with repeated exposures of

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

Table 5: Ratio of early-life to adult cancer po tencies 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 st udies with acute exposures of

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

Table 7. Ratio of early-life to a dult 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 Methodo logy mortality risk model (from U.S. EPA,

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

v i R EFERENCES



# ............................................................................................................................... .... R-1

LIST OF FIGURES

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

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

juvenile to adult cancer potency for carci nogens acting primarily through a mutagenic

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

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

# PREFACE

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

may be conducted differently th an 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 conti nues 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 practi cable and consistent with Agency statutes and

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

Supplemental Guidance is not inte nded to provide any substantiv e or procedural obstacle in

achieving that goal. Therefore, the Supplemen tal 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 EP A has decided in the context of that risk

assessment that the approaches from the Suppl emental 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 fo r guidance only. It does not establish any

substantive “rules” under the Ad ministrative 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 appro ach using estimates from chronic studies (i.e.,

cancer slope factors) with appropr iate modifications to address th e potential for differential risk

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

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

exposure to a carcinogen acting thro ugh a mutagenic mode of action.

The Agency considered both the advantag es and disadvantages of extending the

recommended, age dependent adjustment factors fo r 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., th e use of a linear, no threshold extrapolation

procedure in the absence of data in order to be he alth protective. In gene ral, the Agency prefers

# to rely on analyses of data ra ther than on general defaults. When data are available for a

susceptible lifestage, they should be used directly to evaluate ri sks 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 th e modes of action too

diverse to use this as a category for which a gene ral default adjustment f actor 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-dos e extrapolation approach (without further

adjustment) provides adequate publ ic health conservatism in th e absence of chemical-specific

data indicating differential ea rly-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 pa rtners, to improve understanding

of the implications of earl y life exposure to carcinogens. Development of guidance for

estrogenic agents and chemicals acting through othe r 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 disrup tion will probably require separate analysis.

As the Agency examines additional carcinog enic 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. Pubert y and its associated biological changes, for example, involve

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

carcinogens, depending on their mode of action. The Agency is intere sted 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 elucid ating these lifestages. For each additional

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

differ from those described in this Supplementa l 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 represen tative 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 av ailable to refine the la tter age group. If more

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

may be given to further refinement of these age groups.

vii i

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

and this Supplemental Guidance will be th rough 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. Envi ronmental Protection Agency’s

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

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

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

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

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

those from exposures occurring later in lif e. Evaluating childhood cancer and childhood

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

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

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

Because much of cancer epidemiology addresse s 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 dem onstrates that exposures early in life (i.e.,

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

cancer (reviewed in Toth, 1968; Della Porta a nd Terracini, 1969; Druc kery, 1973; Rice, 1979;

Vesselinovitch et al., 1979; Ri ce 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 alte r the incidence of cancers observed later in life, compared with

the incidence observed with adult-only expos ures (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 ad ults 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 deve lop 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 si milar spectrum of tumors (Hal e 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 hu mans 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 (Gruffe rman, 1998; Israel, 1995). Tumors of childhood

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

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

cancers, soft tissue sarcomas, kidney cancers, ey e cancers, and adrenal gland cancers are the

most common cancers of children, while skin, pros tate, breast, lung, and co lorectal 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 es tablished genetic bases, such

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

1995).

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

guidelines with perinatal 1 

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

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

occurring from chemical exposures is limited (A nderson 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. Pharmacol ogical use of diethylstilbesterol (DES) during

pregnancy to prevent miscarriages induced clea r 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 add ition to the limited human data, there are

examples of transplacental carcinoge ns 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 susceptibility 2 

# to cancer induced by expos ure 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 as corbate (Cohen et al., 1998; Cohen et al.,

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

2 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 “s ensitivity” are used with a variety of definitions in

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

# 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 importan ce 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 tran splacental carcinogens require separate evaluation and are not

quantitatively evaluated in th e analysis presented below.

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

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

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

systems are almost fully developed, though substa ntial 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 w ith chronic later-life dosing; lifetime (i.e., combined perinatal and

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

exposures, such as a single intrap eritoneal (ip) or subc utaneous injection, for both early-life and

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

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

where adult animals only were exposed; some ex amples include diethyln itrosamine (DEN) (Peto

et al., 1984), benzidine (Vesseli novitch et al., 1979), DDT (Ve sselinovitch et al., 1979), and

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

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

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

3 • The sam e tumor sites usually are observed fo llowing either perinatal or adult exposure.

• Perinatal exposure in conjuncti on 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 la ter 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 in creasing 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

# 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). Add itionally, even though not used

quantitatively in the analyses in th is 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 ch emicals (Hayashi et al., 2000), providing

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

carcinogenesis, which uses two doses prior to we aning 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 reas onable expectation that children can be more

susceptible to carcinogenic agents than adul ts (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.

4 • More frequent cell division during developm ent can result in enhanced fixation of

mutations du e to the reduced time availabl e 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 ar e not fully functional during development

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

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

2000).

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

effects later in life (Ande rson 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 ad ults and children with respect to exposure factors such as

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

lifestages are not taken into consid eration because cancer slope factors 3 

# are based upon effects

3 

# Cancer slope factor – An upper bound estimate of the increased can cer risk from a lifetime exposure to an

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

mg/kg-day or ug/m 3 

# ), 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

# observed following exposures to adult humans or se xually mature animals. Since a much larger

database exists for chemicals i nducing cancer in adult humans or se xually mature animals, it is

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

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

undertaken here addresses this i ssue, focusing upon studies that de fine the potential duration and

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

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

description of the procedures us ed, have been published (Bart on et al., 2005). The analysis

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

developing Supplemental Guidance for evaluating can cer susceptibility associ ated with early-life

exposures.

5 upper limit to the true probability.

# 2. PROCEDURES

6 This section describes th e 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 ad ult-only exposures or between ear ly-life-and-adult and adult-only

exposures. Studies were categor ized by length of exposure; th ose studies with quantitative

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

identified. These studies provi ded the basis for quantitativel y estimating the difference in

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

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

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

2.1. DATA SOURCES FO R ANIMAL STUDIES

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

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

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

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

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

Anderson et al. (2000), Miller et al. (2002) and U.S. EPA (1 996). 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 re viewed to determine if a st udy provided information that

could be used for quantitative analysis. The criter ia 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 e liminate 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 eliminat e dose-dependent responses confounding agedependent responses),

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

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

at >1 year for all groups exposed at differe nt ages, where early-lif e 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 e xposure were included (without adjustment) ev en if they also

involved prenatal exposure,

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

comparable to the age at initiation of a st andard 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, beca use 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, a nd adult groups (i.e., studies reporting only

percent response or not includi ng 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 me thods and results from the animal studies

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

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

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

and 3 were used for the calcula tions, described below, for esti mating 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 pr otocol for early-life testing and th e difficulty of standardizing and

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

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

juvenile period, as compared with chronic later-life dos ing; 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 intrap eritoneal (ip) or subc utaneous injection, for both early-life and

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

chronic exposures, and lifetime exposures. Tabl e 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 ch emicals not included in Tables 2 and 3 that

demonstrated carcinogenesis following perinata l 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 positiv e findings) have been studied in the neonatal

mouse assay, but this assay doe s not have a comparable adul t exposure (Flammang et al., 1997;

McClain et al., 2001; Fujii, 1991). Studies across la boratories 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

B6C3F 1 

# mice). Studies of tamoxifen use two Wist ar-derived strains a nd 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 bel ong to this group were not evalua ted quantitatively. In addition,

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

al., 1978). The radiation data were not analyzed in depth, in pa rt 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 si tes in humans with a single exposure involving

all ages, a number of national and internati onal committees of expert s have analyzed and

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

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

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

8 2.2. EVALUATI NG THE MODE OF ACTION OF CARCINOGENS

Evaluation of the mode of action of a car cinogen 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)anthracen e, dimethylnitrosamine, ethylnitrosourea, 3-

methylcholanthrene, methylnitrosour ea, 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, metabo lic profiles, physicochemical properties, and

structure-activity relationship (S AR) analyses in a weight-of-evide nce 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; Mc Carroll 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 r eactive and/or has the

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

# systems for different genetic endpoints, particular ly 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.

9 2.3. QUANTITATIVE M ETHODS

To estimate the potential difference in sus ceptibility 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 tumo r 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 depe nded upon the design of the experiment that

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

exposed either as juveniles or as adults (with eith er 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) P P

0 0 

# ( δ

A 

# = + 1 (

− P 

# ) 1

− e − m A A 

# )

P P

J 

# = + 0 0 

# ( )

1 1

− P 

# (

− e − m A J 

# e λ 

# δ 

# )

where:

subscripts A and J refer to the adult and j uvenile period, respectively,

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

P 0 

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

P

x 

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

m

A 

# is the rate of accumulation of “hits” pe r unit of time for adults, i.e., the cancer

potency, and

δ

x 

# is the duration or number of exposures during age period x

.

For a substantial number of da ta sets (acute exposures), δ J 

# = δ A 

# = 1. We are interested in

# determining λ

, which is the logarithm of the estimated ra tio of juvenile to adult cancer potencies,

a measure of potential suscepti bility for early-life exposure.

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

exposures that were initiated in the juvenile period continue th rough the adult peri od. 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:

P P m m A J



# 0 0 

# ( )

1 1 

# (

e e 

# ( )

A AA



# J 

# = ++ P

− − − λ 

# δ δ

− δ 

# )

. 2) have the same interpre tation as their counterpar (2)

All symbols in (eq ts in (eq. 1), but

now δ J 

# 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 potenti al effect of alternative Baye sian priors that have been

examined) have been published (Barton et al., 20 05). 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 expos ure for each of the juvenile-exposed and adultexposed groups. A few data sets had separate control groups fo r 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 th ree (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 P 0 

# (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 re latively low. (The base of the distribution is

one, as P 0 

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

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

the extra risk

, Q, where the proba

Q

= − 1 e

− m A 

# δ A 

# , Q wa

out the extra risk of

ding to a median or g bility that an animal has a tumor is P 0 

# +(1 – P 0 

# )Q

. 

# So, from

equations 1

, s gi

b ad ul ven a uniform prior on th e interval (0,1), refl ecting total

ignorance a t exposure. Finally, the prior for λ was Gaussian with mean

0 (correspon eometric mean ratio of one) and standard deviation 3. The

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

estimates for the ratio of juvenile to adult po tency. The magnitude of th at influence depends on

10

# the amount of support in the data for different valu es of the log ratio. The prior also effectively

downweights extremely large or sma ll values for the juvenile to a dult potency ratio. Three priors

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

finding the largest prior, i.e., one that would contain the leas t 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 es timates 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 sens itivity analysis showed that this value for the

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

that these data would not influe nce 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 parame ters in these models is the product of

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

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

parameters. This normalization constant was co mputed 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 sta tistical programming la nguage (version 1.8.1; R

Development Core Team, 2003).

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

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

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

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

experiment found that there was less susceptibilit y 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). Th e 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 varian ce. 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 resul ting inverse-variance-weighted m ean yielded inverse-varianceweighted geometric means of ratios.

11

# 2.4. IONIZING RADIATION

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

incidence in adults who were children at th e 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 a nd 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 singl e exposure involving a ll ages. In addition

to the richness of the data, a number of nationa l 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 Scien tific Committee on the Effects of Atomic

Radiation (UNSCEAR, 2000, with Scie ntific Annexes) lists more th an 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 intentionall y or accidentally to some form of ionizing

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

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

et al. (1994), contains detailed data on the incidence of 21 di fferent 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. populati on (U.S. EPA, 1994). It is beyond the scope of

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

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

exposure from UNSCEAR (2000) an d 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 st udies 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 stra ins used make it difficult to compare the

experimental data on cancer i nduction after prenat al irradiation (Preston et al., 2000).

12

# 3. RESULTS

13 3.1. QUALITATIVE EVALUA TION OF THE DATABASE

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

scientif ic data could inform risk assessment po licy 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 impact s 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 postna tal 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 litera ture identified several hundred re ferences reporting more than 50

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

1a) (reviewed in Toth, 1968; Della Porta a nd 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 provide d quantitative data on carcinogenesis following early postnatal

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

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

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

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

single tissues or organs for tumors (e.g., only live r), 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 quantit ative analyses presented later in the results.

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

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

of these studies are notable a nd provide important supporting info rmation. Two recent studies

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

observed following earlier versus later azoxym ethane exposures (Pau lsen et al., 2003).

Shortened mammary tumor latency following estradiol exposure occu rred when exposures

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

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

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

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

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

Newbold et al., 1990, 1997, 1998, 2001). Developmental susceptibilit ies 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), w ith bladder tumors arising when early-life

exposures occurred. Studies with several species, incl uding 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 a nd Ward, 1982; Jurgelski et al., 1979).

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

ideally should address both the period of pot ential 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 inform ation (Figure 1). However, variations in study

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

consistency of effects with di fferent 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 appropr iate for quantitative

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

used subcutaneous or ip injec tion that historically have not been considered quantitatively

relevant routes of environmental exposure fo r 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 du ring 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 al so involved earlier maternal and/or prenatal

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

analysis. Another notable differe nce among studies involved the ti ssues that were evaluated for

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

multiple tissues.

Comparisons within a single repeated dosi ng study may have limitations for evaluating

14

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

lifestages, particularly when dietary or drin king 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 transf er 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-lif e cancer risk arises from higher

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

diphenylhydantoin (DPH) (Chhabr a et al., 1993b) also may resu lt in lower exposure during

lactation, potentially underestimati ng 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 ma y 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, cons istent pathological

evaluation).

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

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

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

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

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

modes of action was further s upported 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 suscepti bility between earlylife and adult exposure was calcula ted as the estimated ratio of cancer potency from early-life

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

quantitative analysis using the st udies that were determined quali tatively to have appropriate

study designs (Tables 2 and 3) cont aining 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 th e 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 mutage nic 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 ac tion with chronic adult dos ing and repeated early

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

distribution. For a Bayesian di stribution, these percentiles func tion in a manner similar to the

95% confidence limits for other type s of statistical analyses. Th e 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-lifest age susceptibility exists for chemicals with

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

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

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

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

the age-dependent responses are not due to di fferences 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 acti on [benzidine, diethylnitrosamine (DEN), 3-

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

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

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

analyzed for benzidine, 3-methylcholanthrene, sa frole, 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 ju venile exposures with each chem ical could be more effective

than adult exposures were at i nducing tumors (Tables 4 and 7; Fi gure 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 carci nogens acting through a mutagenic mode of action).

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

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

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

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

# percentile of the

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

16

# This analysis focused upon the duration of e xposure 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 we aning), drinking water, di et, or inhalation, which

have the potential to deliver diffe rent doses at different lifestag es. 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, weight ed 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., uncer tainty and variability remain. Because these

comparisons include different chemicals with diffe rent 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 geom etric 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 mutageni c mode of action would lead to an increased

tumor incidence compared with adult e xposures 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 availa ble for eight carcinogens with a mutagenic mode of action

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

Diethylnitrosamine (DEN), dimethylbenzanthra cene (DMBA), dimethylnitrosamine (DMN),

ethylnitrosourea (ENU), methyl nitrosourea (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 fe w weeks of life with the identical or sim ilar exposure in young

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

preweaning period (i.e., approxima tely 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 histori cally have not been considered

quantitatively relevant routes of environmenta l 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 in jection route typically alters th e pharmacokinetic time courses of

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

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

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

trends would be similar with ot her routes of exposure. Thes e compounds are expected to be

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

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

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

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

with increased early su sceptibilities up to 178-fo ld (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 susceptibi lity of tumor response

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

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

than later time points, in several cases simila r tumor incidence was obser ved at both these early

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

While the degree of susceptibility generall y declines during the early postnatal period

through puberty into early adult hood, there are exceptions due pe rhaps to pubertal periods of

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

metabolizing enzymes. One such exception was th e 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) re ported 8% mammary tumors following a single dose

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

15% when given once to 26 week old rats. T hus, 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 corre sponds 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 approxi mately two-thirds complete by week 5, consistent with the 5–8

week susceptible period of Meran ze et al. (Silberstein, 2001 ). While this diffe rs from the general

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

earlier. Another example of deviation from the ge neral 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 s hould be noted that th e 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/vagin a. 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 ratio s less than 1 include forestomac h, 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 re sults are difficult to inte rpret, 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 weight ed geometric means for the acute

and for the repeated dosing studies.

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

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

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

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

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

were sufficient to decide that th ey 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 ba sed 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 ch ronic exposures rather th an 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 a nd lifetime studies are mo re appropriate for the

purpose of this analysis.

3.2.2. Carcinogens With Modes of Ac tion Other Than Mutagenicity

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

chronic adult exposures in a single protocol we re available for six ch emicals that do not act

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

ethylene thiourea (ETU), diphenyl hydantoin (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 othe r three evaluated a large number of tissues in

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

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

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

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

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

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

observed from early and/or adult exposures, t hough 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 thyr oid tumors were observed in a dult rats and thyroid, liver, and

pituitary tumors in adult mice. Analysis of th e incidence of tumors pe r 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 chemi cals 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 inciden ce 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 interpre tation of the results is that these studies,

except with DDT and dieldrin, invol ved 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 simila r doses during different

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

in young animals were selected to approximate th e 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 f eeding postnatally to the mother so the young were dosed via

lactation. In addition, DDT, dieldr in, 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 earl y lifestages can be more suscep tible 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, th e UNSCEAR, Annex I (2000) in cludes information derived

from a wide range of both intentional (gener ally diagnostic or th erapeutic medical) and

accidental radiation exposures. Only informati on 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 radi ation 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 ar e extracted from the tables in

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

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

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

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

time of exposure. The larger number of thyroid tu mors 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 me thodology 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 co efficients 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 populat ions. The risk projections we re updated using more recent

vital statistics in a repo rt 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

21 .

Table 11 contains the calculated age-speci fic 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, ski n, and kidney coefficients are

age-independent and only esophageal cancer coeffici ents increase with incr easing age. Also of

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

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

# 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 sampli ng 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

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

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

decision on whether, and if so how, to assess th e 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 studi ed in adult occupational epidem iological studies or chronic

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

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

following perinatal exposures in animals (without adult exposure s), 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 ac tion 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 ch emicals 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 bi oassays with perinatal

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

studies that largely constitute th e available database for this anal ysis. In addition to the chronic

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

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

Two other kinds of information can contri bute toward developi ng a scientifically

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

# Theoretical analyses suggest

that the differential susceptibilit y 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 th e average daily exposure

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

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

provide a concrete example consis tent with these theo retical analyses (Ca ttley et al., 1991;

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

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

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

4 

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

# 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 st udies 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 produc t of concentration and

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

came from the beginning of the exposure rather th an 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 ea rly in the life of the animal (as opposed

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

but the extent to which the differences in tumo r 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 highe st dose used in the two-year

exposure. This latter factor clearly had a signific ant effect for two chemicals, causing tumors at

higher doses that were not observed at lower dos es. These results suggest that pharmacokinetic

or other dose-rate dependencies can make the effects of exposure s at high doses different from

those exposures at lower doses. While not dir ectly informative about early childhood exposures,

these studies provide a perspective on the comm on 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 susceptibil ities to cancer risks for humans exists for

ionizing radiation. The effects of chemical muta gens at different lifestages on cancer induction

are derived from laboratory animal studies. Wh ile the induction of cance r 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 la ter 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 survivor s exhibited different lifestage dependencies at different tumor

sites, though the total radiation- related incidence of tu mors showed a general slow decline with

age at exposure. However, as previously note d, there are apparent differences at some sites

between the two tables. In addition to the sa mpling and modeling differences, the excess risk

values in Table 9 are based on Japanese baselin es 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 radia tion-related tumor incidenc e 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 a nd similarly show some differences

for individual tumor sites. In general, the earl iest 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 ar ound 5–7 weeks) and mice (beginni ng 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 differen tial susceptibility becaus e the exposure rate is

constant at the different ages. The repeated dose studies also include several of the most

informative studies for assessing perinatal carcin ogenesis, 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 include d 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 de sign 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 exposur e 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 cel l 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 di fferent tissues. For example, DMBA appears to

be more effective at initiating mammary tumo rs in 6-8 week old rats, which are undergoing

development of that tissue, than during earlier or later periods (Mer anze et al., 1969). While

tumor promotion processes can be very depe ndent upon the duration of promotion, initiation

processes can occur in relative ly brief periods (e.g., the sing le-dose studies in animals or

radiation exposure in humans). Most tumors take extended periods to develop, making damage

that occurs earlier in lif e more likely to result in tumors prio r to death than w ould exposures that

occur later in life. While some of these observati ons 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 duri ng 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, sh owing an increase in tumor

incidence during perinatal exposure versus expos ures 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 e xposure (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 si ngle-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 biphe nyls were statistically significant. (A

nonstatistically significant incr ease 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 polybr ominated biphenyl studies.

There are important demonstr ations of chemicals acting th rough 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 (C arthew 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 ge nistein 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 f ound uterine tumor development to be dependent

upon early-lifestage exposures (Newbold et al., 2001). Another recent stu dy of estrogen found a

shorter latency for mammary tumors in mice e xposed at 8 and 12 weeks as compared to mice

exposed at 4 or 18 weeks, indicating a suscep tible 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 us ed. The lifetime design has less ability to

26

# distinguish increased su sceptibility from early-lif e exposure than the other types of designs.

Consider two different experime ntal designs. In the first, the “lifetime” design, a group of

animals are exposed starting as juveniles, a nd exposure continues through adulthood. A second

group are exposed only in adulthood, and the juve nile:adult ratio results from a comparison of

tumor incidences in the two groups. In the se cond, the “repeated” de sign, one group of animals

is exposed only during the juvenile period, a nd 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 insensitiv e 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 expos ed 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 (cont rol, juvenile-exposed, adult-exposed groups) in

the two designs is:

Number of animals with tumors

27 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 th e “repeated” design, 16 ju venile-exposed animals

have tumors. The data in the lifetime design are consistent with the hypothesis of no tumors

being induced during the juveni le period: the ratios 36/50 an d 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 allduring the juvenile peri od, 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 th e one-hit model: each additional week of a long

exposure contributes less than th e previous week to th e total number of an imals with tumors.

# Note that, even if the one-hit model is not co rrect, chronic exposure pr obably 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 juveni le period relative to

an exposure in the adult period is the ratio of doses in the tw o periods that give the same

incidence of tumors. However, most of the data sets used in this repo rt contained only one noncontrol dose, precluding the ex tensive dose-response modeling that would be required to

estimate this ratio of doses. However, this do cument largely considered chemicals for which a

mutagenic mode of action has been establis hed 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

P P e a



# a 

# = 1

− 

# ( 1

− 

# )

− m x

0



# P 

# ( ) m j 

# x

j 

# = 1

− 1

− P e −

0



# for dose x . Suppose we want to calculate the dose D

a 

# or D j 

# that results in a given incidence of

tumors after an adult or juven ile exposure. From equation 1, D

a 

# and D j 

# equal:



# ⎛ 1

− P

− c 

# ⎞

ln ⎜ ⎟

⎜ ⎟ ⎝ 1

− P

0 

# ⎠

D

a 

# =

m

a 

# ⎛ 1

− P ⎞

− ln ⎜

c 

# ⎟ ⎜ ⎟ ⎝ 1

− P ⎠

D

= 0

j



# m j



# Thus, the ratio D

a 

# / D

j 

# = m j 

# /m

a 

# , the ratio calculated in this document.

In summary, this analysis supports the conclu sion that there can be greater su sceptibility

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 othe r 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 chemi cals appear to involve different sites when

exposure is during early-life vers us adulthood, an effect that has been observed relatively

infrequently. Development of such approaches would require additional re search to provide an

expanded scientific basis for their support, in cluding additional res earch and the possible

development of new toxicity testing protoc ols that consider early lifestage dosing.

The current data do also not al low 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 expre ss cancers analogous to human childhood cancers. Rigorous

quantification of exposure doses at different lifestages and in rode nt pups in experimental studies

would be useful for evaluating whether th ere is greater child hood susceptibility.

Pharmacokinetic modeling could bett er define the internal doses to improve determination of the

magnitude of increased susceptibility.

29

# 30 5. GUIDANCE FOR ASSE SSING CANCER RISKS

FROM EARLY-LIFE EXPOSURE



# Consistent with the approach and reco mmendations of the U.S. EPA cancer risk

assessment guidelines (U.S. EPA, 2004), any asse ssment of cancer susceptibility will begin with

a critical analysis of th e available information. Figure 3 show s 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 warr ants explicit considerat ion for each assessment.

When developing quantitative estimates of cancer risk, the Agency recommends

integration of age-specific values for both expos ure 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 differe nces in size, physiology, and

behavior. For example, childre n are generally assumed to eat more food and drink more water

relative to their body weight than adults. Children’s normal activitie s, 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 a ll lifestages, including exposures during childhood

and during adulthood. EPA continues to deve lop 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 a nd 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 av ailable 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

# studies that investigate the gene ral properties of the particular mode of action. All data

indicating quantitative differences between chil dren and adults are considered in developing

those portion(s) of the risk es timates 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 extrapolat ion to lower doses such that risk estimates are based on a

lifetime average daily exposure without furthe r 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 th e 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) indica tes 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 quantitativ e differences between children and adults. If

such data are available, an analys is of the differences could be us ed 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

31 5 Determination of chemicals that are operating by a muta genic 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 DN A and can produce such effects as DNA adducts and/or

breakage. Carcinogens with a mutagenic mode of action ofte n 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).

# 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 ac tion (e.g., toxicokinetic or toxicodyna mic 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 appl ying the age-dependent adjustment factors.

If the available, chemical-specific inform ation includes an epidemiologic study of the

effects of childhood exposure or an animal bioass ay 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 chlo ride (U.S. EPA, 2000b; c).

In the absence of early-life st udies on a specific chemical under consideration (Figure 3,

Box 6), the extrapolation from th e point of departure to lower dos es employs linear extrapolation

(see Section 3.3.1 of the U.S. EPA [2005] cancer guidelines). This choi ce is based on mode-ofaction data indicating that mutagens can give rise to can cers 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 ri sk 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 ap pearing later in life. The 10-fold adjustment represents an

approximation of the weighted geometric mean tu mor incidence ratio from juvenile or adult

exposures in the repeated dosing st udies (see Table 8). This adjustment is applied for the first 2

years of life, when toxicokinetic and toxicodyna mic differences between children and adults are

greatest (Ginsberg et al., 2002; Renwick, 1998). Toxicokinetic di fferences from adults, which

are greatest at birth, resolve by approximately 6 months to 1 year, wh ile 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 rapi d 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 ca lculate 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., a pproximately half the difference between 1 and

10 on a logarithmic scale (10 1/2 

# ), between the 10-fold adjustment for the first two years of life

and no adjustment (i.e., 1-fold) for adult expos ure. EPA also recognizes that exposures

occurring near the end of life ma y 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 latenc y 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 expos ures on latency were not evaluate d. Finally, as the adjustment

factors are derived from a weighted geometric mean of the data evaluated, these adjustment will

both over-estimate and under-estimat e the potential potency for ear ly-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 fact ors whenever such data are available.

The following adjustments represent a practical approach that reflect s the results of the

preceding analysis, which concluded that cancer risks generally are higher from early-life

exposure than from similar expos ure durations later in life:

• For exposures before 2 years of age (i.e., span ning 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 sixt eenth birthday), a 3-fold adjustment.

• For exposures after turning 16 years of age, no adjustment.

Clearly other age groups, such as an ag e group experiencing pubertal changes in

physiology, or approximately ages 9 - 15, may ex perience changes in biological processes that

could lead to modifications in the susceptibil ity to the effects of so me carcinogens, depending on

the mode of action. This Supplemental Guidan ce 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 refr actory for carcinogenesis, and beli eves that the mode of action

framework as described by EPA’s cancer guide lines (U.S. EPA, 2005), is an appropriate

mechanism for elucidating these lifestages. In gene ral, the Agency’s analyses of lifestages that

may be susceptible will depend on three factor s: (1) establishing th e mode of action for

carcinogenesis; (2) using knowledge about the biological and toxico logical 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 differen tial risk, which may di ffer significantly from those proposed for the

mutagenic mode of action, are expected to be ev aluated independently of other modes of action.

When data, including well establis hed mode of action data, are available that allow specific

evaluation of lifestage differences in toxicokinetics or toxicodynami cs that would lead to lesser

or greater susceptibility from early-life exposures to carcinogens, then thos e 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 f actor 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 im portant to emphasize that these adjustments are

combined with corresponding age-specific estima tes 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 rele vant 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 averag e 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 can cer risk resulting from

childhood exposure. These adjustments are appl ied 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 adju stment factors to carcinogenic chemicals for which the mode

of action remains unknown. It is the Agency’s l ong-standing science polic y position that use of

the linear low-dose extrapolation approach (without further adju stment) provides adequate public

health conservatism in the absence of chemical -specific data indicati ng differential early-life

susceptibility. At the present time, therefor e, 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 th an 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 DIFFEREN CES IN EXPOSURE AND DOSERESPONSE WHEN ASSESSING CARCINO GEN RISK - SOME EXAMPLES FOR

CARCINOGENS THAT ACT THROUGH A MUTAGENIC MODE OF ACTION



# 36 It is important for the risk assessor to consid er lifestage differences in both exposure and

dose-response when assessing cance r risk resulting from early-lif e exposures. As discussed in

Section 5, age dependent adjustments factors (A DAFs) 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 a ssess total lifetime risk resulting fr om 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 le ss-than-lifetime oral exposures. Risks associ ated with inhalation

exposure to carcinogens that act vi a a mutagenic mode of action are calculated in similar fashion

by applying the appropriate ADAF(s ) along with the corresponding i nhalation 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 abse nt. For all modes of action, when chemicalspecific data are available for early-lif e exposure, those data should be used.

6.1 CALCULATING LIFETIME RISKS ASSO CIATED 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 t ypical 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)

# = 2 x 10 -4



# 37 Example 2 : 

# Now consider the same exposur e scenario for a carcinogen with a mutagenic 

# mode

of action for which the oral cancer slope fact or, 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 exp ectancy 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 m g/kg-d)

x (13yr/70yr)

= 1.1 x 10 -4



# • Risk for ages 16 until 70 = (2 per mg/kg-d) x 1 (A DAF) 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 wh ich exposure rates and/or potencies (slope

# 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 pe r 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



# 38 6.2 CALCULATING LIFETIME RISKS ASSO CIATED 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 pe riod 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.

# Example 3 : 

# If exposure to a carcinog en with a mutagenic mode of action with an oral slope

factor equal to 2 per mg/kg-d occurs during ad ulthood 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 chil dhood, the risk calculations are adjusted to

consider the potential for higher potency from early-lif e exposure. Assessors should remember

that the age dependent adjustment factors for ca rcinogens 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 be tween ages 2 and <16 years:

Risk = 3 (ADAF) x (2 per m g /kg-d) x (0.0001 mg/kg-d) x (5 yr/70 yr)

= 4.3 x 10 -5



# 39 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

# = 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:

40 Risk equals the sum of:

• Risk for birth through < 2 (2yr) = 10 (ADA F) 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 year s 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:

# • Risk for birth through < 2 (2yr) = 10 (ADA F) 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 expos ure 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 expo sure = 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



# 41Standard Rodent Cancer Study: Adult ExposurePostnatal ExposurePostnatal & Adult Exposure (Lifetime)In utero, postnatal, & Adult Exposure (Lifetime)In utero & postnatal ExposurebirthpubertymatingweaningAssessmentof tumorsFigure 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 pr imarily 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 ri ght of each geometric mean correspond to

95% confidence limits. The vertical da rk line represents the inverse-variance weighted geometric mean of the

posterior geometric means. The horizontal dark line represents the 95 th 

# percentile of the unweighted distribution,

with the vertical, dotted line establishing it value.

# Figure 3. Flow chart for early-life risk assessment using mode of action framework

Box 1: Use framework in Cancer Guidelines

to establish MOA(s)

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 exposure inanimals as identified indifferent review articles



# A-1Chemical nameReview articles including prenatal and postnatal exposureChemicalsselected forquantitativeanalysisFujii(1991)McClainet al.(2001)Andersonet al.(2000)Della PortaandTerracini(1969)Otherliterature4-Acetylaminobiphenyl (AAB)X4-Aminoazobenzene (AB)X3-Amino-1,4,-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1)X2-Aminodipyridol[1,2-a:3',2'-d]imidazole (Glu-P-2)X2-Amino-6-methyldipyridol[1,2-a:3',2'-d]imidazole (Glu-P-1)X3-Amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2)XAmitroleXArsenicX5-AzacytidineX3'-Azido-3'-deoxythymidine (AZT)XAzoxymethaneXBenz[a]anthraceneXBenzidineXXBenzo[a]pyrene (BaP)XXX­1 (4'Bromophenylazo)-1-phenyl-1-hydroperoxymethane (BPH)XN-Butyl-N-(3-carboxypropyl)nitrosamine (BCPN)XN-Butyl-N-(3 hydroxbutyl)nitrosamine (BBN)XButylnitrosourea (BNU)XCyclophosphamideXDibenz[a,h]anthracene (DBA)XXDibutylnitrosamine (DBN)XDichlorodiphenyltrichloroethane (DDT)XDieldrinX2-Diethylaminoethyl-2,2-dephenylvalerate hydrochloride(SKF 525A)XTable 1a. Chemicals that have been found to have carcinogenic effects from prenatal or postnatal exposure inanimals as identified in different review articles (continued)Chemical nameReview articles including prenatal andpostnatal exposureChemicalsselected forquantitativeanalysisFujii(1991)McClainet al.(2001)Andersonet al.(2000)Della PortaandTerracini(1969)OtherliteratureDiethylnitrosamine (DEN)XXXDiethylstilbesterol (DES)X4-DimethylaminoazobenzeneX1,2-Dimethylhydrazine (DMH)X7,12-Dimethylbenz[a]anthracene (DMBA)XXXXDimethylnitrosamine (DMN)XXXX5',5'-Diphenylhydantoin (DPH)XEstradiolXX6-Ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (Santoquin)XEthylene thiourea (ETU)XEthyl methane sulphonateXEthylnitrosobiuretXEthylnitrosourea (ENU)XXN-2-Fluorenylacetamide (FAA)XXGenisteinX3-Hydroxyl-4-acetylaminobiphenyl (N-OH-AAB)XN-2-Hydroxy-N-2-fluorenylacetamide (N-OH-FAA)X2-Hydroxypropyl-propylnitrosamineX9-MethylanthraceneXMethyl-2-benzylhydrazineXMethylcholanthreneXX3-Methyl-4-dimethylaminoabenzene (3'ME-DAB)X4-(Methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK)XMethylnitrosourea (NMU)XMethylnitrosourethaneX1-Methyl-3-nitro-1-nitrosoguanidine (MNNG)X



# A-2Table 1a. Chemicals that have been found to have carcinogenic effects from prenatal or postnatal exposure inanimals as identified in different review articles (continued)Chemical nameReview articles including prenatal and postnatal exposureChemicalsselected forquantitativeanalysisFujii(1991)McClainet al.(2001)Andersonet al.(2000)Della PortaandTerracini(1969)Otherliterature2-NaphthylamineX2-NaphthylhydroxyamineXNickel acetateXN-NitrosobuylamineX4-Nitroquinoline-1-oxideXXN-Nitrosomethyl(2-oxopropyl)amineX2-Oxopropyl-propylnitrosamineX1-Phenyl-3,3',-dimethylhydrzineX1-Phenyl-3,3,-dimethyltriazeneXPolybrominated biphenyls (PBBs)XSafrole (3,4-methylenedioxyally benzene)XXXSootXSterigmatocystinXTamoxifenX1,3,5-Trimethyl-2,4,6-tris[3,5-di-tert-butyl-4-hydroxybenzyl]benzene (Ionox 33)XUrethane (ethyl carbamate)XXXVinyl chlorideX



# A-3

# Table 1b. List of chemicals considered in this analysis. (These are chemicals

for which both early-life and adult ex posure 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

(DDT) Vesselinovitch et al. (1979) Repeat dosing

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

(DM BA) 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)

Terracini et al. (1976) Acute exposure

Acute exposure X

Polybrominated biphenyls

(PBBs) Chhabra et al. (1993a) Repeat dosing

Lifetime exposure

Safrole Vesselinovitch et al. (1979) Repeat dosing

Lifetim e exposure X

Urethane Chieco-Bianchi et al. (1963)

Choudari Kommineni et al. (1970)

De Benedictis et al. (1962)

Fiore-Donati et al. (1962) Acute exposure

Acute exposure

Acute exposure

Acute exposure X

Klein (1966) Acute exposure

Lifetime exposure

Liebelt et al. (1964) Acute exposure

Rogers (1 951) Acute exposure

Vinyl chloride (VC) Maltoni et al. (1984) Repeat dosing X

a 

# Formerly known as 20-methylcholanthrene.



# A-4Table 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposuresChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaM FCommentsReferenceAmitroleMiceliverControlNoneControl:N/A90 weeks1/980/96Incidences areVesselinovitch(B6C3F1)0 ppm(1%)(0%)mice with(1983)Gestationday 12Diet, tomothers500 ppmGestation day12 to delivery6/74(8%)b0/83(0%)badenomas orcarcinomas.NewbornDiet, tomothers500 ppmBirth untilweaning10/45(22%)b0/55(0%)bAt weaningDiet, tooffspring500 ppmFrom weaningto 90 weeks20/55(36%)b9/49(18%)bBenzidineMiceliverControlNoneControl:N/A90 weeks1/980/100HigherVesselinovitch et(B6C3F1)0 ppm(1%)(0%)sensitivity inal. (1975b)Gestationday 12Diet, tomothers150 ppmGestation day12 to delivery17/55(31%)c2/62(3%)dmales duringperinatalperiod, inVesselinovitch etal. (1979a)



# A-5NewbornDiet, tomothers150 ppmBirth untilweaning62/65(95%)c2/43(5%)dfemales duringadulthood.At weaningDiet, tooffspring150 ppmFrom weaningto 90 weeks22/50(44%)c47/50(94%)cIncidences aremice withGestationday12Diet, tomothers150 ppmGestation day12 until49/49(100%)c12/48(25%)cadenomas orcarcinomas.weaningGestationDiet, to150 ppmGestation day50/5047/50day 12mothers12 until 90(100%)c(94%)cweeksDDTMiceliverControlNoneControl:N/A90 weeks1/50—VesselinovitchetDichlorodiphenyl­(B6C3F1)0 ppm(2%)al. (1979b)trichloroethaneWeek 1Gavage,daily230 μgWeeks 1–45/49(10%)d—Week5Diet,daily150 ppmWeeks 5–908/49(16%)d—Week 1Gavage,230 μgWeeks 1–9010/50—daily until(20%)c4 weeks,150 ppmthen in(diet)dietTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-6ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFDieldrinMice(B6C3F1)liverControlNoneControl:0 ppmN/A90 weeks1/58(2%)—Vesselinovitch etal. (1979b)Week 1Gavage,daily12.5 μgWeeks 1–43/46(7%)b—Week 5Diet,daily10 ppmWeeks 5–907/60(12%)b—Week 1Gavage,daily until4 weeks,then indiet12.5 μg10 ppmWeeks 1–9021/70(30%)a—DENeDiethylnitrosamineRats(Colworth)liverControlControlN/A29/384(8%)Highest tumorrate when dosedat earlier ages.Incidents arerats withadenomas orcarcinomas.Peto et al. (1984)Week 3Diet (indrinkingwater),daily16 differentdosescombinedfFrom week 3until death6months–3 years105/180(58%)bWeek 6From week 6until death714/1440(50%)bWeek 20From week 20until death76/180(42%)besophagusControlControlN/A0/384(0%)Week 3Diet (indrinkingwater),daily16 differentdosescombinedgFrom week 3until death77/180(43%)bWeek 6From week 6until death663/1440(46%)bWeek 20From week 20until death88/180(49%)bTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-7ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceChhabra et al.(1993b)MFDPHDiphenylhydantoin,5,5-Rats(F344/N)liverControlControl0 ppmN/A2 years0/50(0%)0/50(0%)In rats, perinatalexposure rangedfrom 63 to 630ppm, and adultexposures rangedfrom 240 to 2,400ppm.In mice, perinatalexposure rangedfrom 21 to 210ppm. Adultexposure rangedfrom 30 to 300ppm in males and60 to 600 ppm infemales.Tumor incidencesare animals withadenomas orcarcinomas.PerinatalDiet,daily630ppmPerinatalthrough 8weeks1/50(2%)d0/49(0%)d8 weeks800 ppm8 weeks–2years2/50(4%)d1/50(2%)d8 weeks2,400 ppm8 weeks–2years4/50(8%)d1/50(2%)dPerinatal630–800Perinatalthrough 2 years1/49(2%)d0/50(0%)dPerinatal630–2,400ppmPerinatalthrough 2 years5/49(10%)c0/50(0%)dMice(B6C3F1)liverControlControlmale0 ppmN/A2 years29/50(58%)PerinatalDiet, male210ppmPerinatalthrough 8weeks33/50(66%)d8 weeks100 ppm8 weeks–2years29/49(59%)d8 weeks300 ppm8 weeks–2years26/49(53%)dPerinatal210–100ppmPerinatalthrough 2 years35/49(71%)dPerinatal210–300ppmPerinatalthrough 2 years41/50(82%)cControlControlfemale0 ppmN/A2 years5/48(10.4%)dPerinatalDiet,female210ppmPerinatalthrough 8weeks12/49(24.5%)d8 weeks200 ppm8 weeks–2years14/49(28%)c8 weeks600 ppm8 weeks–2years30/50(60%)cPerinatal210–200ppmPerinatalthrough 2 years16/50(32%)cPerinatal210–600ppmPerinatalthrough 2 years34/50(68%)cTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-8ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFETURatsthyroidControlControl0 ppmN/A2 years1/493/50Tumor incidencesChhabra et al.Ethylene thiourea(F344/N)(2%)(6%)are animals with(1992)PerinatalDiet,daily90ppmPerinatalthrough 84/49(8%)d3/50(6%)dadenomas orcarcinomas.weeks8 weeks83 ppm8 weeks–2years12/46(26%)c7/44(16%)d8 weeks250 ppm8 weeks–237/5030/49years(74%)c(61%)cPerinatal90–83ppmPerinatalthrough 2 years13/50(26%)c9/47(19%)dPerinatal90–250 ppmPerinatal48/5037/50through 2 years(96%)(74%)Mice(B6C3F1)liverControlControl0 ppmN/A2 years20/49(41%)4/50(8%)PerinatalDiet,daily330ppmPerinatalthrough 813/49(26.5%)d5/49(10%)dweeks8 weeks330 ppm8 weeks–232/5044/50years(64%)c(88%)c8 weeks1,000 ppm8 weeks–246/5048/50years(92%)c(96%)cPerinatal330–330Perinatal34/4946/50ppmthrough 2 years(69%)c(92%)cPerinatal330–1,000Perinatal47/4949/50ppmthrough 2 years(6%)c(98%)cthyroidControlControl0ppmN/A1/50(2%)0/50(0%)PerinatalDiet,daily330 ppmPerinatalthrough 81/46(2%)d1/49(2%)dweeks8 weeks330 ppm8 weeks–2years1/49(2%)d2/50(4%)d8 weeks1,000 ppm8 weeks–229/5038/50years(58%)c(76%)cTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-9ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFETUEthylene thioureaPerinatal330–330ppmPerinatalthrough 2 years2/48(4%)d10/49(20%)c(continued)Perinatal330–1,000Perinatal35/4938/50ppmthrough 2 years(71%)c(76%)cpituitaryControlControl0ppmN/A0/44(0%)11/47(23%)PerinatalDiet,daily330ppmPerinatalthrough 80/42(0%)d11/48(23%)dweeks8 weeks330 ppm8 weeks–2years0/42(0%)d19/49(39%)d8 weeks1,000 ppm8 weeks–28/4126/49years(19.5%)c(53%)cPerinatal330–330ppmPerinatalthrough 2 years0/45(0%)d26/47(55%)cPerinatal330–1,000ppmPerinatalthrough 2 years4/39(10%)d24/47(51%)cTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-10AgeAge at deathTumor incidenceChemicalSpecies(strain)TargetsitewhenfirstdosedDose route,# dosesDoseDuration ofexposureMFMFReference3-MethylcholanthreneMiceliverControlgavage, 3×NANA475 days480 days3/390/36Klein (1959)(formerly known as 20-(Albino)per week(7.7%)(0%)methylcholanthrene)8 days0.25 mg/g10×311 days321 days21/25(84%)b7/30(23.3%)b90 days0.25 mg/g10×330 days366 days1/26(3.8%)b0/29(0%)dlungControlNANA475 days480 days17/39(43.6%)14/36(38.9%)8 days0.25 mg/g10×311 days321 days25/25(100%)b28/30(93.3%)b90 days0.25 mg/g10×330 days366 days25/26(96.2%)b27/29(93.1%)bforestomachControlNANA475 days480 days0/39(0%)0/36(0%)8 days0.25 mg/g10×311 days321 days12/25(48%)b12/30(40%)b90 days0.25 mg/g10×330 days366 days13/26(50%)b8/29(27.6%)bskinControlNANA475 days480 days0/39(0%)0/36(0%)8 days0.25 mg/g10×311 days321 days4/25(16%)b4/30(13.3%)b90 days0.25 mg/g10×330 days366 days1/26(3.8%)b1/25(4%)bTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-11ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFPBBsRats (F344/N)livergControlControl0 ppmN/A2 years1/500/50Findings suggestChhabra et al.Polybrominated(2%)(0%)that combined(1993a)biphenylsPerinatalDiet10ppmPerinatal–8weeks5/50(10%)d0/50(0%)dperinatal and adultexposure increasesPBB-relatedhepatocellularcarcinogenicityrelative to adultonly exposure inmice and femalerats.8 weeks10 ppm8 weeks–2years12/49(24%)c12/50(24%)c8 weeks30 ppm8 weeks–2years41/50(82%)c39/50(78%)cPerinatal10–10ppmPerinatal–216/5039/50years(32%)c(78%)cApparentassociationbetweenincreasingincidences ofMCL andexposure to PBBin male andfemale rats.Tumor incidencesare animals withadenomas orcarcinomas.Perinatal10–30 ppmPerinatal–2years41/50(82%)c47/50(94%)cMononuclearcellleukemia(MCL)ControlControl0 ppmN/A2 years25/50(50%)14/50(28%)PerinatalDiet10ppmPerinatal–8weeks31/50(62%)d13/50(26%)d8 weeks10 ppm8 weeks–2years33/50(66%)c22/50(44%)d8 weeks30 ppm8 weeks–2years31/50(62%)d23/50(46%)cPerinatal10–10ppmPerinatal–2years37/50(74%)c27/50(54%)cPerinatal10–30 ppmPerinatal–237/5025/50years(74%)c(50%)cMice (B6C3F1)livergControlControl0 ppmN/A2 years16/50(32%)5/50(10%)PerinatalDiet30ppmPerinatal–840/5021/50weeks(80%)c(42%)c8 weeks10 ppm8 weeks–248/4942/50years(98%)c(84%)c8 weeks30 ppm8 weeks–248/5047/48years(96%)c(98%)cPerinatal10ppmPerinatal–246/4944/50years(94%)c(88%)cPerinatal30–30 ppmPerinatal–250/5047/47years(100%)c(100%)cTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-12ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFSafroleMiceliverControlNoneNoneN/A90 weeks3/1000/100Highest tumor rateVesselinovitch(B6C3F1)(3%)(0%)in males due toet al. (1979b)Day 12 ofgestationGavage, tomothers120 μg/gbodyweight4× (days 12,14,16, 18)2/61(3%)d0/65(0%)dpreweaningtreatment.Highest tumor ratein females due toNewbornGavage, tomothers, on120 μg/gbodyweightFrom birth untilweaning28/83(34%)c2/80(3%)dalternatesusceptibility indaysadulthood.Tumor incidencesare mice withadenomas orcarcinomas.At weaningGavage, tooffspring, 2×weekly120 μg/gbodyweightFrom weaninguntil 90 weeks4/35(11%)d22/36(61%)cDay 12 ofgestationGavage, tomothers,alternatedays120 μg/gbodyweightFrom gestationuntil weaning22/68(32%)b1/72(1%)bDay 12 ofgestationGavage, tomothers,alternate120 μg/gbodyweightFrom gestationuntil 90 weeks19/37(51%)b37/46(80%)bdays untilweaning;Gavage, tooffspring, 2×weeklyUrethaneMice(B6AF1/J)liver1 weekgavage2.5 mg/pup1×39–40weeksTumor incidenceaNo tumor data forcontrols.Klein (1966)MF12/37(33%)b0/40(0%)b1 week2.5 mg/pup16×(1× at 1 week;3× weekly for 5weeks39 weeks11/33(33%)b0/31(0%)bbeginning at 4wks of age)4 weeks2.5 mg/pup15×(3× weekly for5 weeks41 weeks0/37(0%)b0/31(0%)bbeginning at 4weeks of age)Table 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFVCVinyl chlorideRats (SpragueDawley)liverangiosarcomaControlControl0 ppmN/A135weeks0/22(0%)0/29(0%)Higher tumor riskwhen exposed atbirth, higher forfemales.Maltoni et al.(1984)NewbornInhalation6,000 ppm4 hrs/day,5 days/wk,5 weeks124weeks5/18(28%)b12/24(50%)b10,000ppm6/24(25%)b9/20(45%)bWeek 136,000ppm4 hrs/day,5 days/wk, 52weeks135weeks3/17(18%)b10/25(40%)b10,000ppm3/21(14%)b4/25(16%)bzymbalglandControlControl0ppmN/A135weeks0/28(0%)0/29(0%)NewbornInhalation6,000ppm4 hrs/day,5 days/wk,5 weeks124weeks1/12(8%)b1/17(6%)b10,000ppm1/17(6%)b0/17(0%)bWeek 136,000 ppm4 hrs/day,5 days/wk, 52weeks135weeks3/29(10%)b4/30(13%)b10,000ppm10/30(33%)b6/30(20%)bleukemiaControlControl0ppmN/A135weeks0/27(0%)1/29(3%)NewbornInhalation6,000ppm4 hrs/day,5 days/wk,5 weeks124weeksN/A1/7(14%)b10,000ppm2/6(33%)b0/15(0%)bWeek 136,000 ppm4 hrs/day,5 days/wk, 52weeks135weeksN/A0/29(0%)b10,000ppm0/27(0%)b2/29(7%)bnephroblastomaControlControl0 ppmN/A135weeks0/22(0%)0/29(0%)NewbornInhalation6,000ppm4 hrs/day,5 days/wk,5 weeks124weeks0/15(0%)b0/21(0%)b10,000ppm0/19(0%)b0/17(0%)b



# A-13Table 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)



# A-14ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFVCVinyl chlorideWeek 136,000 ppm4 hrs/day,5 days/wk, 52135weeks4/18(22%)b1/26(4%)b(continued)weeks10,000ppm3/21(14%)b2/25(8%)bangio-ControlControl0ppmN/A1350/290/29sarcomas:weeks(0%)(0%)other sitesNewbornInhalation6,000ppm4 hrs/day,5 days/wk,124weeks1/15(7%)b0/21(0%)b10,000ppm5 weeks0/19(0%)0/17(0%)bWeek 136,000 ppm4 hrs/day,5 days/wk, 52135weeks1/29(3%)b2/30(7%)b10,000ppmweeks2/30(7%)b1/30(3%)bangiomasandControlControl0ppmN/A135weeks0/28(0%)2/29(7%)bfibromas:other sitesNewbornInhalation6,000ppm4 hrs/day,5 days/wk,124weeks1/15(7%)b0/21(0%)b10,000ppm5 weeks2/19(11%)b1/17(6%)bWeek 136,000 ppm4 hrs/day,5 days/wk, 52135weeks2/29(7%)b2/30(7%)b10,000ppmweeks2/29(7%)b1/29(3%)bhepatomaControlControl0ppmN/A135weeks0/19(0%)0/28(0%)NewbornInhalation6,000ppm4 hrs/day,5 days/wk,124weeks9/18(50%)b11/24(46%)b10,000ppm5 weeks13/24(54%)b7/20(35%)bWeek 136,000 ppm4 hrs/day,5 days/wk, 52135weeks0/10(0%)b1/17(6%)b10,000ppmweeks1/8(13%)b0/16(0%)bTable 2. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult repeated exposures(continued)ChemicalSpecies(strain)Target siteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathMTumorsaFCommentsReferenceVCVinyl chloride(continued)skincarcinomasControlNewbornControlInhalation0ppm6,000ppm10,000ppmN/A4 hrs/day,5 days/wk,5 weeks135weeks124weeks0/20 1/29(0%) (3%)1/10 1/14(10%)b(7%)b1/160/15(6%)b(0%)bWeek 136,000 ppm10,000ppm4 hrs/day,5 days/wk, 52weeks135weeks0/15 2/19(0%)b(11%)b2/131/21(15%)b(5%)bneuroblastomaControlControl0ppmN/A135weeks0/22 0/29(0%) (0%)



# A-15NewbornInhalation6,000ppm10,000ppm4 hrs/day,5 days/wk,5 weeks124weeks0/18 0/29(0%)b(0%)b0/220/19(0%)b(0%)bWeek 136,000 ppm10,000ppm4 hrs/day,5 days/wk, 52weeks135weeks2/21 1/27(10%)b(4%)b2/225/26(9%)b(19%)baWhere not delineated by gender, data combined by study authors or gender not specified. Where percentages only are given, number of subjects not specified.bNot evaluated by authors.cSignificant compared with controls.dEvaluated but not significant compared with controls.eReported as NDEA (N-nitrosodiethylamine) in the original document.fResults from each dose are not available.gTumors were adenomas or carcinomas.Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure



# A-16ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFBaPMiceliverControlControlNoneN/A142 weeks7/1001/100In general, hepatomasVesselinovitchBenzo[a]pyrene(B6C3F1)(7%)(1%)developed withet al. (1975a)Day 1i.p.75 μg/gbodyweight1×86weeks(m)129 weeks(f)26/47(55%)b3/45(7%)bsignificantly higherincidence (p<0.01) inmice that were treatedwithin 24 hours of birthor at 15 days of age150 μg/gbodyweight1×81weeks(m)121 weeks51/63(81%)b8/45(18%)bthan they did insimilarly treatedanimals at 42 days of(f)age.+ higherfor males.Day 15i.p.75 μg/gbodyweight1×93weeks(m)116 weeks(f)36/60(60%)b4/55(7%)b150 μg/gbody weight1×81weeks(m)32/55(58%)b4/55(7%)b90 weeks (f)Day 42i.p.75 μg/gbodyweight1×108weeks(m)7/55(13%)b0/47(0%)b150 μg/gbody weight1×87weeks(m)4/47(9%)b0/46(0%)bMiceliverControlControlNoneN/A142 weeks8/1001/100+ higher for males.(C3AF1)(8%)(1%)Day 1i.p.75μg/gbody weight1×80weeks(m)91 weeks (f)21/62(34%)b1/45(2%)b“Age at death” is theaverage age at whichtumors were observed.150 μg/gbodyweight1×69weeks(m)24/52(46%)b1/56(2%)b701 weeks(f)Day 15i.p.75 μg/gbodyweight1×90weeks(m)15/56(27%)b1/49(2%)b102 weeks(f)Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-17ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFBaPBenzo[a]pyrene150μg/gbodyweight1×77weeks(m)12/53(23%)b1/57(2%)b(continued)62 weeks (f)Day 42i.p.75μg/gbodyweight1×0/30(0%)b0/32(0%)b150 μg/gbody weight1×79weeks(m)1/32(3%)c0/40(0%)bMicelungControlControlControlN/A142 weeks13/1009/100Both sexes developed(B6C3F1)(13%)(9%)lung tumors with higherDay 1i.p.75 μg/gbody weight1×103weeks(m)126 weeks(f)20/47(43%)b22/45(49%)bincidence when treatedwith BaP at birth than at15 or 42 days of age(p<0.05).150 μg/gbodyweight1×84weeks(m)37/63(59%)b28/45(62%)b112 weeks(f)Day 15i.p.75 μg/gbodyweight1×103weeks(m)15/60(25%)b18/55(33%)b122 weeks(f)150 μg/gbody weight1×82weeks(m)20/55(36%)b18/45(40%)b101 weeks(f)Day 42i.p.75 μg/gbody weight1×119weeks(m)20/55(36%)b12/47(26%)b131 weeks(f)150 μg/gbody weight1×95weeks(m)18/47(38%)b8/46(17%)b118 weeks(f)Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFBaPBenzo[a]pyrene(continued)Mice(C3AF1)lungControlControlNoneN/A142 weeks60/100(60%)50/100(50%)Of the two mousestrains tested, C3AF1mice developedsignificantly moretumors than did theB6C3F1mice(p<0.001).Vesselinovitch etal. (1975a)Day 1i.p.75μg/gbody weight1×78weeks(m)82 weeks (f)58/62(93%)b42/45(93%)b150 μg/gbody weight1×70weeks(m)73 weeks (f)48/52(92%)b52/56(93%)bDay 15i.p.75μg/gbody weight1×87weeks(m)98 weeks (f)52/56(93%)b46/49(94%)b150 μg/gbody weight1×75weeks(m)79 weeks (f)50/53(94%)b52/57(91%)bDay 42i.p.75μg/gbody weight1×91weeks(m)93 weeks (f)28/30(93%)b28/32(87%)b150 μg/gbody weight1×85weeks(m)83 weeks (f)28/32(87%)b36/40(90%)bDBADibenzanthraceneMice(Caracul × Pstock)lungControlControlNoneN/A228 days1/31(3.2%)Law(1940)Day 1i.p.4 mg percm3vehicle1×181days24/24(100%)b2 monthss.c.4 mg percm3vehicle1×189days2/29(6.9%)b



# A-18Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-19ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFDENDiethylnitrosamineMice(B6C3F1)liverControlControlVehicle(0.01 mLtrioctanoin/gbody weight)4×142weeks(m)1377/98(7%)1/100(1%)Animals treated asnewborns and infantsdeveloped significantlymore liver tumors thanVesselinovitch etal. (1984)weeks (f)animals that wereDay 1i.p. (3-, 6­and 6-dayintervals)1.5 μg/gbody weight4×67weeks(m)90 weeks(f)37/51(73%)b45/64(70%)btreated as young adults.Newborns and infantfemales developed livertumors at a later age3 μg/g bodyweight4×65weeks(m)80 weeks40/58(69%)b44/65(68%)bthan similarly treatedmales.(f)Incidences forDay 151.5 μg/gbody weight4×86weeks(m)117weeks (f)41/57(72%)b40/71(56%)bmalignant tumors only.3 μg/g bodyweight4×76weeks(m)48/69(70%)b46/62(74%)b96 weeks(f)Day 421.5 μg/gbody weight4×117weeks(m)1359/49(18%)b1/47(2%)bweeks (f)3 μg/g bodyweight4×123weeks(m)1336/38(16%)b4/57(7%)bweeks (f)Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-20ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFDENMiceliverControlControlVehicle (0.14×1238/991/97Highest tumor rateVesselinovitch etDiethylnitrosamine(C3AF1)trioctanoin/gweeks(8%)(1%)when dosed at earlyal. (1984)(continued)body weight)(m)ages.131weeks(f)Newborns and infantDay 1i.p. (3-, 6­and 6-dayintervals)1.5 μg/gbody weight4×64weeks(m)84 weeks(f)23/32(72%)b11/39(28%)bfemales developed livertumors at a lowerincidence than similarlytreated males.+ higher for males.3 μg/g bodyweight4×59weeks(m)39/58(67%)b26/50(52%)b76 weeks(f)Day 151.5μg/gbodyweight4×82weeks(m)22/46(48%)b8/65(12%)b102weeks (f)3 μg/g bodyweight4×74weeks(m)35/54(65%)b22/62(35%)b94 weeks(f)Day 421.5μg/gbodyweight4×105weeks(m)10612/56(22%)b0/53(0%)bweeks (f)3 μg/g bodyweight4×105weeks(m)1039/57(16%)b0/56(0%)bweeks (f)Mice(B6C3F1)lungControlControlVehicle (0.1trioctanoin/gbodyweight)4×142weeks(m)137weeks (f)13/98(13%)9/100(9%)The mice treated asnewborns showed lungtumors earlier thananimals exposed atother times. It is notknown whether this wasdue to actual earlieremergence of tumors orTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-21ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFDENDiethylnitrosamineDay 1i.p. (3-, 6­and 6-day1.5 μg/gbody weight4×70weeks(m)29/51(57%)b49/64(77%)bto their earlier detectioncaused by shorter(continued)intervals)91 weekssurvival.(f)3 μg/g bodyweight4×68weeks(m)34/58(59%)b42/65(65%)b81 weeks(f)Day 151.5μg/gbodyweight4×87weeks(m)51/57(89%)b61/71(86%)b115weeks (f)3 μg/g bodyweight4×77weeks(m)51/69(74%)b53/62(85%)b97 weeks(f)Day 421.5μg/gbodyweight4×123weeks(m)12938/49(78%)b38/47(81%)bweeks (f)3 μg/g bodyweight4×121weeks(m)12733/38(87%)b43/57(75%)bweeks (f)Mice(C3AF1)lungControlControlVehicle (0.1trioctanoin/g4×142weeks60/99(61%)50/97(52%)Of the two strains,C3AF1mice developedbody weight)(m)137weekslung tumors with ahigherincidence and(f)multiplicity thanDay 1i.p. (3-, 6­and 6-day1.5 μg/gbody weight4×65weeks(m)30/32(94%)b38/39(97%)bB6C3F1hybrids.intervals)84 weeks(f)3 μg/g bodyweight4×59weeks(m)49/58(84%)b46/50(92%)b76 weeks(f)Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)AgeTumorsaDosewhenSpeciesTargetroute,Duration ofAge atfirstChemical(strain)site# doses DoseexposuredeathComments ReferencedosedM FDENDay 151.5μg/g4× 80weeks42/46 61/65Diethylnitrosaminebody weight(m)(91%)b(94%)b(continued)101weeks (f)3 μg/g body4× 74weeks50/54 57/62weight(m)(93%)b(92%)b92 weeks(f)Day 421.5 μg/g4× 10455/56 52/53body weightweeks(98%)b(98%)b(m)110weeks (f)3 μg/g body4× 10156/57 54/56weightweeks(98%)b(96%)b(m)102weeks (f)MiceliverControl Control None N/A90 weeks1/980/96Infant animals of bothVesselinovitch(B6C3F1)(1%) (0%)sexes (Day 15) wereand Mihailovichmore sensitive than(1983)Gestationi.p. 1.5 μg/g1× 2/501/51similarly exposedday 18body weight(4%)b(2%)badults.Day 15i.p. (3-, 6-1.5 μg/g4× 47/5160/64and 6-daybody weight(92%)b(94%)bintervals)Day 421.5 μg/g4×13/493/47body weight(26%)b(6%)bDay 1i.p.1.5μg/g1× 73weeks 15/59—At the 1.5-μg doseVesselinovitch etbody weight(25%)blevel, 1-day-old miceal. (1979a)developed significantly5 μg/g body1×29/45—fewer liver tumors thanweight(64%)bsimilarly treated infants10 μg/g1×24/25—(Day 15) (p<0.025).body weight(96%)bTumor incidence inDay 15 i.p. 1.5 μg/g1×13/24—treated groups versusbody weight(54%)bcontrols was not5 μg/g body1×40/54—evaluated.weight(74%)b



# A-22Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)AgeTumorsaDosewhenSpeciesTargetroute,Duration ofAge atfirstChemical(strain)site# doses DoseexposuredeathComments ReferencedosedM FDEN10μg/g1×25/25—Diethylnitrosaminebody weight(100%)b(continued)DMBARatsmammaryDay 20 Gavage 10 mg/100 g1× Week25— 3/636 of 42 (86%) animalsRusso et al. (1979)Dimethyl-(Sprague­ adeno­body weight(50%)bdosed at age 20 daysbenz[a]anthraceneDawley)sarcomadied soon after.Day 3010 mg/100 g1× Week26 — 14/15Highest number ofbody weight(93%)btumors per animal wasDay 4010 mg/100 g1× Week27 — 8/9in the 46-day group,body weight(89%)bwith decreasingnumbers in the olderDay 4610 mg/100 g1× Week28 — 8/8animals.body weight(100%)bDay 5510 mg/100 g1× Week29 — 33/34Animals were sacrificedbody weight(97%)b22 weeks aftertreatment.Day 7010 mg/100 g1× Week32 — 5/8body weight(63%)bDay 14010 mg/100 g1× Week42 — 10/15body weight(67%)bDay 18010 mg/100 g1× Week47 — 14/26body weight(54%)bRatsmammaryControlControl None N/A 170/22 0/25Highest tumor rate inMeranze et al.d(Wistar)carcinoma5–8months(0%) (0%)females exposed at 5–8(1969)weeksweeks.ControlControl None N/A 200/31 2/20Animals were observed26 weeksmonths(0%)(10%)for 16 months following< Week 2Gavage0.5–1.0 mg 1×Week 40–0/23 4/50treatment.56(0%)b(8%)bWeek 5–815 mg 1×Week 14–0/2314/2555(0%)b(56%)bWeek 2615 mg 1×Week 32–0/34 4/2673(0%)b(15%)bRats (Wistar,mammaryWeek 5–8Gavage15 mg 1×Week 14–0/21 0/22castrated)carcinoma55(0%)b(0%)bWeek 2615 mg 1×Week 32–0/33 0/2673(0%)b(0%)b



# A-23Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)AgeTumorsaDosewhenSpeciesTargetroute,Duration ofAge atfirstChemical(strain)site# doses DoseexposuredeathComments ReferencedosedM FDMBARatsTotal tumorsControlControl None N/A 170/22 0/25Total tumors includesDimethyl-(Wistar)5–8months(0%) (0%)leukemia.benz[a]anthraceneweeks(continued)ControlControl None N/A 202/31 5/2026 weeksmonths(6%)(25%)< Week 2Gavage0.5–1.0 mg 1×Week 40–16/23 36/5056(70%)b(72%)bWeek 5–815 mg 1×Week 14–7/2316/2555(30%)b(64%)bWeek 2615 mg 1×Week 32–12/34 13/2673(35%)b(50%)bMicelung Control:ControlAqueous1× 40weeks 0/127/2315 μg DMBA gave riseWalters (1966)(BALB/c)Day 1s.c.gelatine(0%)(30%)to a significantly greaterincidence of lungDay 1 s.c. 15 μg 1×40 weeksf14/1424/24tumors when(100%)b(100%)badministered toWeek 2–3s.c.15μg1× 42–4312/23 16/22newborn mice than to(suckling)weeks(52%)b(73%)bsuckling or youngadults.s.c. 30 μg2× 42–4314/14 24/24(60 μg total)weeks(100%)b(100%)bAdultes.c.15μg1× 48-496/1215/33weeks(50%)b(45%)bs.c.30μg2× 48-499/1021/23(60 μg total)weeks(90%)b(91%)bs.c. 30 μg6× 48-4912/12 13/13(180 μgweeks(100%)b(100%)btotal)Mice(Swiss)lymphomaControl Control None N/A 31–523/408Higher tumor rates atPietra et al. (1961)weeks(0.7%)younger age ofexposure.Day 1 i.p. 30–40 μg 1×13–336/31weeks(19%)bOnly one treatmentDay 1 s.c. 30–40 μg 1×12–278/27group was exposed i.p.;weeks(30%)bothers were exposed bys.c. injection..Week 8 s.c. 900 μg 1×30 weeks1/13(8%)b



# A-24Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)AgeTumorsaDosewhenSpeciesTargetroute,Duration ofAge atfirstChemical(strain)site# doses DoseexposuredeathComments ReferencedosedM FDMBAMice (Swiss) lungControl Control None N/A 31–524/408Dimethyl-weeks(0.9%)benz[a]anthraceneDay 1 i.p. 30–40 μg 1×13–3324/31(continued)weeks(77%)bDay 1 s.c. 30–40 μg 1×12–2723/27weeks(85%)bWeek 8 s.c. 900 μg 1×30 weeks2/13(15%)bDMNRatskidneyDay 1i.p.20 mg/kg 1×≥51/33 (3)bIn the neonatal group,Hard (1979)Dimethyl-(Wistar)carcinomamonthsthe dose was reduced toDay 2130 mg/kg 1×5/39 (13)bnitrosamine20 mg/kg to achieveMonth 130 mg/kg 1×2/33 (6)bapproximatelyequivalent numbers ofMonth 1.530 mg/kg 1×1/28 (4)bsurvivors.Month 230 mg/kg 1×1/26 (4)bNo control group.Month 330 mg/kg 1×10/27 (37)bMonth 430 mg/kg 1×7/32 (22)bMonth 530 mg/kg 1×0/14 (0)bRatskidneyDay 1 i.p. 20 mg/kg 1×≥51/33 (3)b(Wistar)adenomamonthsDay 2130 mg/kg 1×13/39 (33)bMonth 130 mg/kg 1×11/33 (33)bMonth 1.530 mg/kg 1×13/28 (48)bMonth 230 mg/kg 1×11/26 (42)bMonth 330 mg/kg 1×18/27 (67)bMonth 430 mg/kg 1×17/32 (53)bMonth 530 mg/kg 1×6/14 (43)b



# A-25Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)SpeciesTargetChemical(strain)siteDMNRatskidneyDimethyl-(Wistar)mesenchymalnitrosaminetumors(continued)Ratskidney(Wistar)corticalepithelialtumorsRatsTotal tumors(Wistar)AgewhenfirstdosedDay 1Day 21Month 1Month 1.5Month 2Month 3Month 4Month 5Day 1Day 21Month 1Month 1.5Month 2Month 3Month 4Month 5Day 1Day 21Month 1Month 1.5Month 2Month 3Month 4Month 5Doseroute,# dosesi.p.i.p.i.p.Dose20 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg20 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg20 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kg30 mg/kgDuration ofexposure1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×1×Age atdeath≥5months≥5months≥5monthsTumorsaM8/33 (24)b18/39 (46)b23/33 (70)b5/28 (19)b2/26 (8)b3/27 (11)b7/32 (22)b0/14 (0)b2/33 (6)b16/39 (41)b12/33 (36)b14/28 (52)b11/26 (42)b18/27 (67)b21/32 (66)b6/14 (43)b11/33 (33)b25/39 (64)b25/33 (76)b17/28 (63)b13/26 (50)b18/27 (67)b22/32 (69)b7/14 (50)bFCommentsMesenchymal tumorswere most frequent inthe three youngest agegroups (z test,p < 0.001).ReferenceHard (1979)



# A-26Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFENUEthylnitrosoureaRatsnervoussystemDay 1Injection20 mg/kg1×100%bSusceptibility to neurooncogenic effectdeclined with increasingMaekawa andMitsumori (1990)Day 30Injection20 mg/kg1×61%bage.Mice(B6C3F1)liverControlControlNoneN/A90 weeks1/98(1%)0/96(0%)Both male and femalemice were responsive toexposure duringprenatal and infant life.Vesselinovitch(1983)Gestationday 18i.p.60 μg/gbody weight1×28/52(54%)b18/49(37%)bDay 1560 μg/gbody weight1×41/50(82%)b28/51(55%)bDay 4260 μg/gbody weight1×10/50(20%)b5/50(10%)bRats(Wistar)nerve tissueControlControlNoneN/A4–7months0/16(0%)0/10(0%)Highest tumor rate seenwhen exposed duringgestation or soon afterbirth.Statistically significantdecrease in tumorincidence withincreasing age ofexposure.Naito et al. (1981)Gestationday 16i.p.s.c.40 mg/kg1×26/26(100%)b18/18(100%)bDay140mg/kg1×12/12(100%)g16/16(100%)gWeek140mg/kg1×12/17(71%)b18/20(90%)bWeek240mg/kg1×10/14(71%)b14/18(78%)bWeek340mg/kg1×6/13(46%)b5/17(29%)bWeek440mg/kg1×8/15(53%)b2/10(20%)b



# A-27Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-28ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumorsaCommentsReferenceMFENUEthylnitrosourea(continued)Mice(B6C3F1)lungDay 1i.p.60 μg/g bodyweight1×49/55(89%)b49/50(98%)bVesselinovitch etal. (1974)Day 151×50/55(91%)b47/55(85%)bDay 421×53/59(90%)b44/51(86%)bDay 1120 μg/g bodyweight1×36/38(95%)b54/60(90%)bDay 151×45/49(92%)b43/50(86%)bDay 421×52/54(96%)b50/57(88%)bMice(C3AF1)lungDay 160 μg/g bodyweight1×46/47(98%)g51/51(100%)gDay 151×49/49(100%)g57/59(97%)gDay 421×59/59(100%)g57/57(100%)gDay 1120 μg/g bodyweight1×63/64(98%)g53/57(93%)gDay 151×54/56(96%)g50/56(89%)gDay 421×59/59(100%)g48/48(100%)gMice(B6C3F1)liverDay 1i.p.60 μg/g bodyweight1×50/54(93%)g28/43(65%)gDay 151×55/56(98%)g33/54(61%)gDay 421×12/40(30%)b6/39(15%)bDay 1120 μg/g bodyweight1×29/34(85%)g32/53(60%)gDay 151×45/48(94%)g29/43(67%)gDay 421×17/49(35%)g4/50(8%)gTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-29ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumorsaCommentsReferenceMFENUEthylnitrosourea(continued)Mice(C3AF1)liverDay 1i.p.60 μg/g bodyweight1×42/45(93%)g19/41(46%)gDay 151×42/50(84%)g19/48(40%)gDay 421×7/29(24%)b4/50(8%)bDay 1120 μg/g bodyweight1×55/62(89%)g19/45(42%)gDay 151×35/45(78%)g15/35(43%)gDay 421×8/33(24%)b3/33(9%)bMice(B6C3F1)kidneyDay 1i.p.60 μg/g bodyweight1×11/48(23%)b5/49(10%)bDay 151×6/41(15%)b7/31(23%)bDay 421×4/40(10%)b3/37(8%)bDay 1120 μg/g bodyweight1×10/30(33%)g14/53(26%)bDay 151×17/37(46%)g19/49(39%)bDay 421×8/40(20%)b11/39(28%)bMice(C3AF1)kidneyDay 1i.p.60 μg/g bodyweight1×7/44(16%)b6/45(13%)bDay 151×7/41(17%)b8/46(17%)bDay421×3/42(42%)b3/43(7%)bDay1120 μg/g bodyweight1×4/52(7%)b6/29(21%)gDay151×8/35(23%)b12/29(41%)gDay 421×6/41(71%)b3/39(8%)bTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-30ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumorsaCommentsReferenceMFENUEthylnitrosourea(continued)Mice(B6C3F1)HarderianDay 160 μg/g bodyweight1×7/40(17%)b5/43(12%)bDay 151×10/51(20%)b17/59(29%)bDay421×14/50(28%)b14/45(31%)bDay1120 μg/g bodyweight1×9/30(30%)g6/52(12%)bDay151×15/41(37%)g8/31(26%)bDay 421×25/48(52%)g14/49(29%)bMice(C3AF1)HarderianDay160 μg/g bodyweight1×3/25(12%)b4/35(11%)bDay151×1/9(11%)b6/38(16%)bDay421×12/48(25%)b5/33(15%)bDay1120 μg/g bodyweight1×3/52(6%)b1/25(4%)bDay151×6/46(13%)b2/52(4%)bDay 421×5/29(17%)b2/11(18%)bMice(B6C3F1)stomachDay 160 μg/g bodyweight1×3/48(6%)b4/43(9%)bDay 151×10/42(24%)g7/45(16%)bDay421×9/51(18%)g8/36(22%)bDay1120 μg/g bodyweight1×2/29(7%)b9/53(17%)bDay151×10/35(29%)g12/33(36%)bDay 421×12/53(23%)g12/50(24%)bTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-31ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumorsaCommentsReferenceMFENUEthylnitrosourea(continued)Mice(C3AF1)stomachDay 160 μg/g bodyweight1×2/39(5%)b7/45(16%)bDay 151×7/45(16%)g7/38(18%)bDay421×14/55(25%)g7/49(14%)bDay1120 μg/g bodyweight1×8/60(13%)b9/44(20%)bDay151×16/51(31%)g11/42(26%)bDay 421×19/48(40%)g13/37(35%)bMice(B6C3F1)malignantlymphomasDay160 μg/g bodyweight1×2/55(4%)b6/52(12%)gDay151×3/56(5%)b14/59(24%)gDay421×9/59(15%)b17/59(29%)gDay1120 μg/g bodyweight1×8/39(20%)b15/65(23%)gDay151×14/60(23%)b17/58(29%)gDay 421×12/59(20%)b14/60(23%)gMice(C3AF1)malignantlymphomasDay 160 μg/g bodyweight1×6/49(12%)b8/49(16%)gDay 151×3/49(6%)b13/61(21%)gDay421×6/60(10%)b9/55(16%)gDay1120 μg/g bodyweight1×3/66(5%)b10/58(17%)gDay151×10/56(18%)b18/60(30%)gDay 421×3/49(6%)b13/50(26%)gTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumor incidenceaCommentsReferenceMFNMUMethylnitrosoureaMice(BC3F1)Total tumorsControlControlN/AN/A60 weeks1/20(5%)0%Control mice did notexhibit tumors in targetsites except a singlehepatoma in a malecontrol mouse.Terracini andTesta (1970)lungDay 1i.p.50 μg/g bodyweight1×60 weeks12/15(80%)b16/19(84%)b5weeks50 μg/g bodyweight1×60 weeks10/26(39%)b10/35(29%)blymphosarcomaDay 150 μg/g bodyweight1×60 weeks23/39(59%)b23/45(51%)b5weeks50 μg/g bodyweight1×60 weeks11/35(31%)b21/45(47%)bliverDay 150 μg/g bodyweight1×60 weeks10/12(83%)b1/17(6%)b5weeks50 μg/g bodyweight1×60 weeks0%b0%ckidneyDay 150 μg/g bodyweight1×60 weeks3/15(20%)b3/18(17%)b5weeks50 μg/g bodyweight1×60 weeks2/21(10%)b0%cfore-stomachDay 150 μg/g bodyweight1×60 weeks0%b4/17(24%)b5weeks50 μg/g bodyweight1×60 weeks8/22(36%)b12/18(67%)bRats(Wistar)mammaryDay 1i.p.50 μg/g bodyweight1×60 weeks0%b4/14(29%)bTumor incidence forcontrol rats was basedon previousexperiments (DellaPorta et al., 1968) andwas not specificallyreported in this paper.Terracini andTesta (1970)5weeks50 μg/g bodyweight1×60 weeks0%b3/5(60%)blymphosarcomaDay 150 μg/g bodyweight1×60 weeks1/10(10%)b0%b5weeks50 μg/g bodyweight1×60 weeks2/8(25%)b1/11(9%)bkidney (anaplastic)Day 150 μg/g bodyweight1×60 weeks14/18(78%)b9/13(69%)b5weeks50 μg/g bodyweight1×60 weeks2/5(40%)b5/12(42%)b



# A-32Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumor incidenceaCommentsReferenceMFNMUMethylnitrosourea(continued)kidney(adenoma)Day 150 μg/g bodyweight1×60 weeks3/14(21%)b2/6(33%)b5weeks50 μg/g bodyweight1×60 weeks1⁄4(25%)b0%bforestomachDay 150 μg/g bodyweight1×60 weeks4/14(29%)b3/6(50%)b5weeks50 μg/g bodyweight1×60 weeks0%c0%bintestineDay 150 μg/g bodyweight1×60 weeks3/10(30%)b2/2(100%)b5weeks50 μg/g bodyweight1×60 weeks2/4(50%)b0%bMice(C3Hf/Dp)thymuscontroli.p.NANA120wks**0/34(0%)0/25(0%)*Age at death fromthymic lymphomareported specifically forsome, but not all, dosegroups.**Control mice weresacrificed at 120 wks.***Age of death for allmice in this dose group,regardless of cancertype.Terracini et al.(1976)Day 125 μg NMU/gbody weight1×29 ± 8.4wks2/16(13%)b5/25(20%)bDay 7025 μg NMU/gbody weight1×120wks(M)***100 wks(F)0/20(0%)c1/20(5%)bDay 150 μg NMU/gbody weight1×16.5 ± 0.7wks16/24(67%)b30/44(68%)bDay2150 μg NMU/gbody weight1×24.5 ± 2.5wks14/44(32%)b18/38(47%)bDay 7050 μg NMU/gbodyweight1×31.4 ± 4.4wks9/30(30%)b6/41(15%)b



# A-33Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-34ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge at deathTumor incidenceReferenceMFMFNMUMethylnitrosourea(continued)Mice(C3Hf/Dp)extra-thymiclymphomacontroli.p.NANA120weeks120weeks1/34(3%)2/25(8%)Terracini et al. (1976)Day 125 μg NMU/gbodyweight1×100weeks90weeks2/16(13%)b1/25(4%)bDay 7025 μg NMU/gbody weight1×120weeks100weeks0/20(0%)b0/20(0%)bDay 150 μg NMU/gbody weight1×70weeks80weeks0/24(0%)b0/44(0%)bDay 2150 μg NMU/gbody weight1×100weeks90weeks1/44(2%)b0/38(0%)bDay 7050 μg NMU/gbody weight1×110weeks90weeks1/30(3%)b0/41(0%)blungcontroli.p.NANA120weeks120weeks4/34(12%)6/25(24%)Day 125 μg NMU/gbodyweight1×100weeks90weeks7/16(44%)b13/25(52%)bDay 7025 μg NMU/gbody weight1×120weeks100weeks12/20(60%)b8/20(40%)bDay 150 μg NMU/gbody weight1×70weeks80weeks5/24(21%)b11/44(25%)bDay 2150 μg NMU/gbody weight1×100weeks90weeks23/44(52%)b15/38(39%)bDay 7050 μg NMU/gbody weight1×110weeks90weeks18/30(60%)b24/41(59%)blivercontroli.p.NANA120weeks120weeks13/34(38%)1/25(4%)Terracini et al. (1976)Day 125 μg NMU/gbodyweight1×100weeks90weeks9/16(56%)g2/25(8%)bDay 7025 μg NMU/gbody weight1×120weeks100weeks12/20(60%)g2/20(10%)bDay 150 μg NMU/gbody weight1×70weeks80weeks4/24(17%)g3/44(7%)bDay 2150 μg NMU/gbody weight1×100weeks90weeks21/44(48%)g1/38(2.6%)bTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-35ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge at deathTumor incidenceReferenceMFMFNMUMethylnitrosourea(continued)Mice(C3Hf/Dp)Day 7050 μg NMU/gbody weight1×110weeks90weeks8/30(27%)g2/41(5%)bstomachcontroli.p.NANA120weeks120weeks0/34(0%)5/25(20%)Day 125 μg NMU/gbodyweight1×100weeks90weeks2/16(13%)b10/25(40%)bDay 7025 μg NMU/gbody weight1×120weeks100weeks3/20(15%)b7/20(35%)bDay 150 μg NMU/gbody weight1×70weeks80weeks2/24(8%)b1/44(2%)bDay 2150 μg NMU/gbody weight1×100weeks90weeks19/44(43%)b9/38(24%)bDay 7050 μg NMU/gbody weight1×110weeks90weeks8/30(27%)b21/41(51%)bkidneycontroli.p.NANA120weeks120weeks0/34(0%)0/25(0%)Terracini et al. (1976)Day 125 μg NMU/gbody weight1×100weeks90weeks0/16(0%)b0/25(0%)bDay 7025 μg NMU/gbody weight1×120weeks100weeks0/20(0%)b0/20(0%)bDay 150 μg NMU/gbody weight1×70weeks80weeks0/24(0%)b4/44(9%)bDay 2150 μg NMU/gbody weight1×100weeks90weeks1/44(2%)b4/38(11%)bDay 7050 μg NMU/gbody weight1×110weeks90weeks5/30(17%)b7/41(17% )bTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)



# A-36ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge at deathTumor incidenceReferenceMFMFNMUMethylnitrosourea(continued)Mice(C3Hf/Dp)ovarycontroli.p.NANA120weeks120weeksNA3/25(12%)Day 125 μg NMU/gbodyweight1×100weeks90weeksNA2/25(8%)bDay 7025 μg NMU/gbody weight1×120weeks100weeksNA4/20(20%)bDay 150 μg NMU/gbody weight1×70weeks80weeksNA0/44(0%)bDay 2150 μg NMU/gbody weight1×100weeks90weeksNA9/38(24%)bDay 7050 μg NMU/gbody weight1×110weeks90weeksNA16/41(39%)bmammarycontroli.p.NANA120weeks120weeksNA2/25(8%)Terracini et al. (1976)Day 125 μg NMU/gbody weight1×100weeks90weeksNA1/25(4%)bDay 7025 μg NMU/gbody weight1×120weeks100weeksNA0/20(0%)bDay 150 μg NMU/gbody weight1×70weeks80weeksNA0/44(0%)bDay 2150 μg NMU/gbody weight1×100weeks90weeks1/44(2%)b0/38(0%)bDay 7050 μg NMU/gbody weight110weeks90weeksNA4/41(9.8%)buterusorvaginacontroli.p.NANA120weeks120weeksNA1/25(4%)Day 125 μg NMU/gbody weight1×100weeks90weeksNA1/25(4%)bDay 7025 μg NMU/gbody weight1×120weeks100weeksNA6/20(30%)bDay 150 μg NMU/gbody weight1×70weeks80weeksNA0/44(0%)bDay 2150 μg NMU/gbody weight1×100weeks90weeksNA1/38(3%)bDay 7050 μg NMU/gbody weight110weeks90weeks7/41(17%)bTable 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)DoseTumorsaSpeciesTargetAge whenDuration ofAge atroute,Chemical(strain)sitefirst dosedDoseexposuredeathComments Reference# dosesM FUrethane MicelungNewborn s.c. 0.18 mg/g1× 10weeks 100%bThe average numberKaye and Trainin(SWR)adenomabody weightof tumors per mouse(1966)increased linearly11–22 weeks s.c. 0.25 mg/g1× 23–340%bwith dose.body weightweeksMiceliverControl Control None N/A 493 days14/97 1/77Liebelt et al. (1964)(C3H/f)(m)(14%)(1%)553 days(f)Day 1 i.p. 0.8 mg/g1× 481days27/30 18/39body weight(m)(90%)g(46%)g434 days(f)8–10 weeks i.p. 1 mg/g body1× 321days6/25 0/32weight(m)(24%)c(0%)c-lungControl Control None N/A 493 days0/97 0/77The number of lung(m)(0%) (0%)tumors among the553 dayscontrols was not(f)provided.Day 1 i.p. 0.8 mg/g1× 401days14/30 19/39body weight(m)(46%)g(48%)g408 days(f)8–10 weeks i.p. 1 mg/g body1× 506days2/25 0/32weight(m)(8%)c(0%)c-reticularControl Control None N/A 493 days2/97 6/77tissue(m)(2%) (8%)553 days(f)Day 1 i.p. 0.8 mg/g1× 285days4/3022/39body weight(m)(13%)c(56%)g343 days(f)8–10 weeks i.p. 1 mg/g body1× -0/25 4/32weight453 days(25%)c(13%)c(f)



# A-37Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)DoseTumorsaSpeciesTargetAge whenDuration ofAge atroute,Chemical(strain)sitefirst dosedDoseexposuredeathComments Reference# dosesM FUrethaneMiceleukemia Control Control None N/A 8–101%Highest tumor ratesFiore-Donati et al.(continued)(Swiss)monthswhen dosed at birth.(1962)Day 1 s.c. 2 mg in 0.051×13/60Exposure tomL aqueous(22%)bnewborns wassolutionfollowed by 21.6%Day 54 mg in 0.051×7/39leukemia, occurringmL aqueous(18%)bat a mean age of 105solutiondays.Day 4020 mg in 0.11×2/63mL aqueous(3%)bsolutionMicelungControlControl None N/A 9 weeks 0/15—The proportion ofRogers (1951)(Swiss)adenoma2 weeks(0%)animals withadenomas decreasedControlControl None N/A 11 weeks 0/14—steadily with age of4 weeks(0%)exposure.ControlControl None N/A 13 weeks 1/15—6 weeks(7%)ControlControl None N/A 15 weeks 2/15—8 weeks(13%)ControlControl None N/A 17 weeks 0/15—10 weeks(0%)2 weeks i.p.1 mg/g body1× 9weeks 24/24—weight(100%)b4 weeks i.p. 1 mg/g body1× 11weeks 23/25—weight(92%)b6 weeks i.p.1 mg/g body1× 13weeks 22/25—weight(88%)b8 weeks i.p. 1 mg/g body1× 15weeks 21/25—weight(84%)b10 weeks i.p. 1 mg/g body1× 17weeks 19/25—weight(76%)b



# A-38Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAge whenfirst dosedDoseroute,# dosesDoseDuration ofexposureAge atdeathTumorsaCommentsReferenceMFUrethane(continued)Mice(Swiss)lungadenoma3 weeksi.p.0.25 mg/gbody weight1×12weeks16/19(84%)b—0.5mg/gbody weight1×12 weeks16/20(80%)b—1 mg/g bodyweight1×12weeks18/20(90%)b—8 weeksi.p.0.25mg/gbody weight1×17weeks4/17(24%)b—0.5mg/gbody weight1×17 weeks15/16(94%)b—1 mg/g bodyweight1×17 weeks18/18(100%)b—



# A-39Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumor incidenceaCommentsReferenceMFUrethane(continued)Mice(Swiss)liverControlControlN/AN/A360–720days10/227(4.4%)4/222(8.22%)Chieco-Bianchi etal. (1963)Day 1s.c.1 mg/g bodyweight1×180 days1/20(5%)g0/20(0%)cDay 1s.c.1 mg/g bodyweight1×240 days2/17(12%)g0/12(0%)cDay 1s.c.1 mg/g bodyweight1×300 days5/18(28%)g0/16(0%)cDay 1s.c.1 mg/g bodyweight1×360 days11/20(55%)g0/23(0%)cDay 1s.c.1 mg/g bodyweight1×420 days13/15(87%)g2/22(9%)gDay 1s.c.1 mg/g bodyweight1×480 days17/23(74%)c2/25(8%)cDay 5s.c.1 mg/g bodyweight1×420 days9/13(69.2%)b2/11(18.2%)bDay 20s.c.1 mg/g bodyweight1×420 days1/13(8%)b0/16(0%)bDay 40s.c.1 mg/g bodyweight1×420 days0/11(0%)b0/9(0%)bMice(Swiss)skinControlControlN/AN/A180–550days30/712(4.21%)Croton oil treatmentinitiated at 40 days ofage.Chieco-Bianchi etal. (1963)Day1s.c.1mgurethane/gbody weight;5% croton oilsingledoseurethane,croton oilapplied2×/weekfor 10mos660 days26/59(44.1%)g



# A-40Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumor incidenceaCommentsReferenceMFUrethane(continued)Day40s.c.1mgurethane/gbody weight;5% croton oilsingledoseurethane,croton oilapplied2×/weekfor 10mos700 days8/41(19.5%)bMice(B6AF1/J)liverControlgavageN/AN/A71weeks1/25(4%)0/25(0%)Klein(1966)Day 11 mg/g bodyweight1×66 weeks9/20(45%)g9/26(35%)gDay 71 mg/g bodyweight1×67 weeks20/22(91%)g20/26(77%)gDay 141 mg/g bodyweight1×68 weeks16/20(80%)g10/23(43%)gDay 211 mg/g bodyweight1×69 weeks13/23(57%)g1/20(5%)gDay 281 mg/g bodyweight1×70 weeks4/24(17%)g1/20(5%)glungControlgavage1mg/gbodyweight1×71 weeks9/25(36%)6/25(24%)Day 11 mg/g bodyweight1×66 weeks20/20(100%)b25/26(96%)bDay 71 mg/g bodyweight1×67 weeks22/22(100%)b26/26(100%)bDay 141 mg/g bodyweight1×68 weeks19/20(95%)b19/23(83%)bDay 211 mg/g bodyweight1×69 weeks23/23(100%)b19/20(95%)bDay281mg/gbodyweight1×70 weeks24/24(100%)b20/20(100%)bMice(B6AF1/J)HarderianglandControlgavage1 mg/g bodyweight1×71 weeks0/25(0%)0/25(0%)Klein(1966)Day 11 mg/g bodyweight1×66 weeks0/20(0%)c1/26(4%)b



# A-41Table 3. Methodological information and tumor incidencefor animal studies with early postnatal and juvenileand adult acute exposure (continued)ChemicalSpecies(strain)TargetsiteAgewhenfirstdosedDoseroute,# dosesDoseDurationofexposureAge atdeathTumor incidenceaCommentsReferenceMFUrethane (continued)Day 71 mg/g bodyweight1×67 weeks0/22(0%)c1/26(4%)bDay 141 mg/g bodyweight1×68 weeks0/20(0%)c2/23(9%)bDay 211 mg/g bodyweight1×69 weeks1/23(4%)b0/20(0%)cDay 281 mg/g bodyweight1×70 weeks0/24(0%)c0/20(0%)cforestomachControlgavage1mg/gbodyweight1×71 weeks0/25(0%)1/25(4%)Day 11 mg/g bodyweight1×66 weeks0/20(0%)c3/26(12%)bDay 71 mg/g bodyweight1×67 weeks1/22(5%)b1/26(4%)bDay 141 mg/g bodyweight1×68 weeks1/20(5%)b4/23(17%)bDay 211 mg/g bodyweight1×69 weeks0/23(0%)c1/20(5%)bDay 281 mg/g bodyweight1×70 weeks2/24(8%)b1/20(5%)baWhere not delineated by gender, data combined by study authors or gender not specified. Where percentages only are given, number of subjects not specified.bNot evaluated by authors.cEvaluated but not significant compared with controls.dStudy also included mammary fibroadenomas andfibromas as well as other types of cancers.e8–9 weeks old.fIncludes survivors up to 40 weeks only.gSignificant compared with controls.i.p. = intraperitoneal injection;s.c. = subcutaneous injection



# A-42Table 4. Ratio of early-life to adult cancer potenciesfor studies with repeated exposures of juvenile and adultanimals to carcinogens witha mutagenic mode of action*



# A-43UnweightedSpeciesgeometricCompound(strain)SexDoseTumormean2.5%Median97.5%ReferenceBenzidineMice (B6C3F1)maleliver11164110198Vesselinovitch et al.(1975b)femaleliver0.160.0040.221.13-MU3-Methylcholanthrene(formerly known as 20­methylcholanthrene)Mice (Albino)male0.25 mg/ghepatoma337.430268Klein (1959)female0.25mg/ghepatoma7.71.17.185male0.25mg/gforestomach0.910.390.912.1female0.25mg/gforestomach1.50.581.54.2male0.25mg/gskin1.80.0482.122female0.25mg/gskin1.50.0231.821SafroleMice(B6C3F1)maleliver471644198Vesselinovitch et al.(1979b)femaleliver0.120.0020.181.1VCVinyl chlorideRats (SpragueDawley)male6,000 ppmliver-angiosarcoma6.70.0359.857Maltoni et al. (1984)male10,000 ppmliver-angiosarcoma7.40.0351162female6,000ppmliver-angiosarcoma134.91333female10,000ppmliver-angiosarcoma308.729121male6,000ppmzymbal gland0.730.00321.130male10,000ppmzymbal gland0.270.00220.45.4female6,000ppmzymbal gland0.480.00270.716female10,000ppmzymbal gland0.150.00140.194.5male10,000ppmleukemia210.02637514female6,000ppmleukemia1.30.00351.7153female10,000ppmleukemia0.290.00190.3517male6,000ppmnephroblastomas0.150.00140.194.8male10,000ppmnephroblastomas0.170.00150.216.2female6,000ppmnephroblastomas0.280.00180.3316female10,000 ppmnephroblastomas0.240.00170.2911male6,000ppmangiosarcomasother sites0.90.00331.2653male10,000ppmangiosarcomas-0.250.00170.3012Table 4. Ratio of early-life to adult cancer potenciesfor studies with repeated exposures of juvenile and adultanimals to mutagenicchemicals (continued)



# A-44UnweightedSpeciesgeometricCompound(strain)SexDoseTumormean2.5%Median97.5%Referenceother sitesVCfemale6,000ppmangiosarcomas-0.240.00170.2911Vinyl chlorideother sites(continued)female10,000ppmangiosarcomasother sites0.320.00190.3820male6,000 ppmangiomas &0.720.00311.033fibromas-othersitesmale10,000 ppmangiomas &1.40.00452.3647fibromas-othersitesfemale6,000 ppmangiomas &0.270.00180.3316fibromas-othersitesfemale10,000 ppmangiomas &0.520.00240.6341fibromas-othersitesmale6,000ppmhepatoma621158543male10,000 ppmhepatoma348.232218female6,000ppmhepatoma551351352female10,000ppmhepatoma558.453513male6,000 ppmskin carcinomas1.10.00351.582male10,000 ppmskin carcinomas0.410.00240.5615female6,000 ppmskin carcinomas0.460.00240.5924female10,000 ppmskin carcinomas0.310.00190.3719male6,000ppmneuroblastoma0.210.00160.269.5male10,000ppmneuroblastoma0.200.00160.248.5female6,000ppmneuroblastoma0.270.00180.3215female10,000ppmneuroblastoma0.140.00140.184.4*The 2.5% and 97.5% are percentilesof the posterior distribution. For a Bayesian distribution, thesepercentiles function inamanner similar to the 95% confidence limits for other types of statistical analyses.Table 5. Ratio of early-life to adult cancer potencies forstudies with repeated exposures of juvenile and adult animalsto chemicals with a nonmutagenic mode of action*



# A-45Ratio of juvenile to adult potencyUnweightedSpeciesgeometricCompound(strain)SexDoseTumormean2.5%Median97.5%ReferenceAmitroleMice (B6C3F1)maleNAliver135.11430Vesselinovitch (1983)femaleNAliver0.140.00130.183.9DDTMice (B6C3F1)maleNAliver1.30.00442.525Vesselinovitch et al.(1979a)DieldrinMice (B6C3F1)maleNAliver0.750.00311.227Vesselinovitch et al.(1979a)DPHRats (F344/N)male630liver0.40.00240.5416Chhabra et al. (1993b)female630liver0.240.00170.2912Mice(B6C3F1)male210liver1.50.00402.471female210liver1.30.00562.615ETURats (F344/N)male90thyroid0.370.00290.615.4Chhabra et al. (1992)female90thyroid0.230.00180.37.0Mice(B6C3F1)male330liver0.0910.00110.121.9female330liver0.0570.00100.0810.65male330thyroid0.410.00220.5225female330thyroid0.40.00240.5516male330pituitary0.320.00190.3822female330pituitary0.240.00180.326.9PBBRats(F344/N)male10liver0.590.00411.16.6Chhabra et al. (1993a)female10liver0.0630.00090.0791.2male10mononuclearcell leukemia0.790.00351.418female10mononuclearcell leukemia0.210.00170.286.0Mice(B6C3F1)male30liver3.91.93.97.5female30liver1.00.371.052.1*The 2.5% and 97.5% are percentilesof the posterior distribution. For a Bayesian distribution, thesepercentiles function inamanner similar to the 95% confidence limitsfor other types of statistical analyses.Table 6. Ratio of early-life to adult cancer potencies for studies with acute exposures of juveniles and adult animals tocarcinogens with a mutagenic mode of action*



# A-46CompoundSpecies(strain)SexDoseTumorDayRatio of juvenile to adult potencyReferenceUnweightedgeometricmean2.5%Median97.5%BaP*Mice (B6C3F1)male75 μg/kgliver1day9.32.98.455Vesselinovitch et al.(1975a)15days113.59.661female75 μg/kg1day1.20.00831.63115days1.70.0152.136male150 μg/kg1day298.22619415days154.113109female150 μg/kg1day8.81.48.19415days1.20.00821.630Mice (C3AF1)male75 μg/kgliver1day112.11011215days7.51.17.083female75 μg/kg1day0.20.00180.269.115days0.20.00170.248.5male150 μg/kg1day143.012.813015days3.60.113.849female150 μg/kg1day0.20.00170.248.815days0.20.00170.248.7Mice(B6C3F1)Male75 μg/kglung1 day1.20.451.23.415days0.20.00460.311.4female75 μg/kglung1 day2.81.0962.79.515days1.40.411.45.1Male150 μg/kglung1 day2.21.02.15.415days0.80.20.822.3female150 μg/kglung1 day7.92.67.24315days3.71.13.422Mice(C3AF1)male75 μg/kglung1 day1.20.471.23.215days1.10.431.083.1Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-47CompoundSpecies(strain)SexDoseTumorDayRatio of juvenile to adult potencyReferenceUnweightedgeometricmean2.5%Median97.5%BaP*(continued)female75 μg/kglung1 day1.60.661.554.015days1.60.711.634.2male150 μg/kglung1 day1.50.571.55.015days1.90.711.86.0female150 μg/kglung1 day1.30.611.32.915days1.20.541.12.6DBAMicelung178201435100Law (1940)DEN**Mice (B6C3F1)male6 μg/kgliver1 day9.03.58.337Vesselinovitch et al.(1984)15days8.93.58.236female6 μg/kgliver1 day359.13123915days256.3226175male12 μg/kgliver1 day9.63.38.85015days9.83.48.951female12 μg/kgliver1 day165.9156715days197.11879Mice(C3AF1)male6 μg/kgliver1 day7.32.96.92615days3.51.43.313female6 μg/kgliver1 day173.21616615days6.40.866.073male12 μg/kgliver1 day113.79.55315days9.83.48.950female12 μg/kgliver1 day408.53634015days255.022221Mice(B6C3F1)male6 μg/kglung1 day0.50.270.520.9315days1.60.951.62.7female6 μg/kglung1 day0.90.540.891.515days1.20.761.22.0Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-48Ratio of juvenile to adult potencyCompoundSpecies(strain)SexDoseTumorDayUnweightedgeometricmean2.5%Median97.5%ReferenceDEN**(continued)male12 μg/kglung1 day15days0.40.70.210.390.400.660.731.1female12 μg/kglung1 day0.70.440.731.215days1.40.881.42.3Mice(C3AF1)male6 μg/kglung1 day0.70.220.671.715days0.50.210.561.3female6 μg/kglung1 day1.10.451.12.515days0.70.360.741.5male12 μg/kglung1 day0.30.0840.330.7615days0.60.260.621.4female12 μg/kglung1 day0.70.350.751.615days0.70.370.751.5DMBA#Rats (Wistar)maletotal2 vs 5–8 wks3.31.33.210Meranze et al. (1969)2 vs 26 wks3.21.33.19.7femaletotal2 vs 5–8 wks1.30.681.32.52 vs 26 wks3.31.23.016mammary2 vs 5–8 wks0.00.00120.0560.262 vs 26 wks0.20.00230.295.35 vs 26 wks7.11.86.455Mice (Balb/c)male15 μglung1 day302.8221482Walters (1966)15–19 days1.00.281.03.5male30 μgx2lung15–19 days141.05610978female15 μglung1 day606.046235015–19 days3.10.513.022female30 μgx2lung15–19 days151.2111004Mice (Swiss)lymphoma2.70.602.519Pietra et al. (1961)lung9.12.98.740Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-49CompoundSpecies(strain)SexDoseTumorDayRatio of juvenile to adult potencyReferenceUnweightedgeometricmean2.5%Median97.5%DMN***Rats (Wistar)3 wkstotal1 month0.70.410.731.3Hard (1979)1.5months1.10.581.12.12months1.50.751.53.03months0.90.500.941.824 hr1 month0.30.130.280.61.5months0.40.180.420.92months0.60.240.561.33months0.40.160.360.781 month1.5 months1.50.801.523.02months2.01.02.04.23months1.30.691.32.5ENUMice (B6C3F1)maleliver7.83.97.718Vesselinovitch (1983)female7.12.96.921Rats (Wistar)malenerve tissue1 day272.5201374Naito et al. (1981)1week1.60.611.64.62weeks1.60.581.64.83weeks0.70.120.722.3female1day646.05024881weeks9.62.68.9592weeks6.21.65.7403weeks0.70.00900.898.9Mice (B6C3F1)male60 μg/glung11.00.601.01.7Vesselinovitch et al.(1974)151.10.661.11.8female60μg/glung12.11.172.14.1151.00.601.01.7male120μg/glung11.00.601.01.7Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-50CompoundSpecies(strain)SexDoseTumorDayRatio of juvenile to adult potencyReferenceUnweightedgeometricmean2.5%Median97.5%15 1.1 0.661.01.8ENUfemale120μg/g lung 1 2.1 1.22.14.1(continued)15 1.0 0.601.01.7Mice(C3AF1) male 60 μg/g lung 1 8.7 2.78.04815 52 5.2392141female 60μg/g lung 15 0.7 0.320.721.6male 120μg/g lung 1 0.9 0.380.922.215 0.7 0.280.671.6female 120μg/g lung 1 0.5 0.240.541.215 0.4 0.180.420.92Mice(B6C3F1) male 60 μg/g liver 1 8.8 4.28.52215 14 6.21437female 60 μg/g liver 1 6.3 2.66.11815 5.6 2.45.416male 120μg/g liver 1 5.2 2.55.11115 7.6 3.97.517female 120μg/g liver 1 11 4.1114615 14 4.91355Mice(C3AF1) male 60 μg/g liver 1 12 4.7114315 8.1 3.27.629female 60 μg/g liver 1 7.5 2.67.03215 4.8 1.84.618male 120μg/g liver 1 9.8 4.19.33215 6.6 2.76.323female 120μg/g liver 1 5.4 1.75.02515 5.4 1.75.125Mice(B6C3F1) male 60 μg/g kidney 1 2.2 0.732.18.015 1.2 0.291.25.1Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-51Ratio of juvenile to adult potencyUnweightedSpeciesgeometric97.5Compound(strain)Sex Dose Tumor Daymean 2.5% Median%Referencefemale 60μg/g kidney 1 0.7 0.0240.855.915 2.6 0.612.515ENUmale120μg/gkidney 1 1.70.651.74.4(continued)15 2.6 1.142.66.4female 120μg/g kidney 1 0.9 0.370.872.015 1.4 0.671.43.2Mice(C3AF1) male 60 μg/g kidney 1 1.8 0.171.91515 2.0 0.252.016female 60μg/g kidney 1 1.0 0.0161.31315 2.1 0.162.220male 120μg/g kidney 1 0.2 0.00290.241.515 1.5 0.381.55.9female 120μg/g kidney 1 2.3 0.172.42015 7.1 1.86.547Mice(B6C3F1) male 60 μg/g Harderian 1 0.3 0.0180.411.415 0.5 0.0750.521.4female 60μg/g Harderian 1 0.1 0.00250.160.7415 0.8 0.350.842.0male 120μg/g Harderian 1 0.4 0.130.420.9615 0.6 0.260.571.2female 120μg/g Harderian 1 0.1 0.00300.180.8515 0.7 0.170.772.1Mice(C3AF1) male 60 μg/g Harderian 1 0.1 0.00230.201.315 0.1 0.00160.181.8female 60μg/g Harderian 1 0.4 0.0190.522.515 0.8 0.150.853.4male 120μg/g Harderian 1 0.1 0.00100.0861.015 0.3 0.00500.402.8Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-52Ratio of juvenile to adult potencyCompoundSpecies(strain)SexDoseTumorDayUnweightedgeometricmean2.5%Median97.5%Referencefemale120μg/gHarderian10.10.00120.0941.2150.10.00120.0810.90ENU(continued)Mice (B6C3F1)male60 μg/gstomach1150.31.90.00910.610.341.822.48.7female60μg/gstomach10.20.00830.261.1150.20.00720.241.0male120μg/gstomach10.20.00590.200.90151.20.501.22.9female120μg/gstomach10.60.190.601.5151.60.671.63.7Mice(C3AF1)male60 μg/gstomach10.00.00090.0630.51150.30.0230.411.3female60μg/gstomach10.80.0850.893.5151.10.191.14.5male120μg/gstomach10.20.0100.190.56150.70.320.701.5female120μg/gstomach10.40.140.461.2150.60.240.641.5NMUMice (BC3F1)malefemale50 μg/g50 μg/glung adenomaslung adenomas113.46.31.32.43.36.09.323Terracini and Testa(1970)male50μg/glymphosarcoma12.51.12.46.4female50μg/glymphosarcoma11.10.491.12.4male50μg/ghepatoma1356.532324female50μg/ghepatoma10.30.00230.3913male50 μg/grenal adenoma10.90.00931.213female50 μg/grenal adenoma11.30.00811.733male50μg/gforestomach10.00.00060.0390.52female50μg/gforestomach10.10.00270.150.69Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)Ratio of juvenile to adult potencyUnweightedSpeciesgeometric97.5Compound(strain)Sex Dose Tumor Daymean 2.5% Median%ReferenceMice (C3Hf/Dp) male 25 μg/g thymic1 1.9 0.0482.123lymphomaNMUfemale25μg/gthymic1 1.2 0.00891.530(continued)lymphomamale 25 μg/g lung adenomas 11.0 0.0131.211female 25 μg/g lung adenomas 10.4 0.0180.461. 7male 25 μg/g liver tumor 10.2 0.00160.214.6female 25 μg/g liver tumor 10.3 0.00260.394.4male25μg/gStomach 1 0.50.00450.676.8female 25μg/g Stomach 1 0.3 0.00460.433.8ovarian 1 0.1 0.00140.173.5uterine/vaginal 1 8.6 1.18.197male 50μg/g thymic1 7.9 3.17.430lymphomafemale 50μg/g thymic1 3.1 1.33.07.8lymphomamale 50 μg/g lung adenomas 10.04 0.00080.0580.45female 50 μg/g lung adenomas 10.1 0.00120.0840.53male 50 μg/g liver tumor 10.2 0.00210.337.8female 50 μg/g liver tumor10.1 0.00110.134.5male 50μg/g Stomach 1 0.01 0.00030.0130.12female 50μg/g Stomach 1 0.1 0.00220.150.96ovarian 1 0.0 0.00030.0140.14uterine/vaginal 1 0.0 0.00050.0340.46male 50μg/g thymic21 4.3 1.64.117lymphomafemale 50μg/g thymic21 1.0 0.391.02.6lymphomamale 50 μg/g lung adenomas 210.1 0.00220.221.1female 50 μg/g lung adenomas 210.7 0.300.751.7



# A-53Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-54CompoundSpecies(strain)SexDoseTumorDayRatio of juvenile to adult potencyReferenceUnweightedgeometricmean2.5%Median97.5%male50 μg/gliver tumor210.10.00130.154.3female50 μg/gliver tumor210.90.00511.423NMU(continued)male50μg/gstomach210.10.0010.080.64female50μg/gstomach211.80.771.84.7ovarian210.00.00070.0550.97uterine/vaginal211.70.591.76.4UrethaneMice (Swiss)male1 mg/gliver1244.421220Chieco-Bianchi et al.(1963)female1mg/gliver10.40.00440.5413male1mg/gliver5142.413137female1mg/gliver51.20.0171.426male1mg/gliver200.20.00180.2810female1mg/gliver200.10.00110.124.8both1mg/gskin10.20.00270.325.4Urethane +croton oilMice (Swiss)both1 mg/gskin12.91.22.88.2UrethaneRats (MRCWistar-derived)male/female16%×6neurilemmomas10.20.00280.334.5Choudari Kommineni etal. (1970)male/female16%×6neurilemmomas280.40.00450.516.3male/female16%×6liver17.91.47.182male/female16%×6liver280.20.00260.411.7male/female16%×6thyroid10.00.00060.0390.67male/female16%×6thyroid280.10.00110.11.5Mice(Swiss)male/female1 mg/glung1151.211997De Benedictis et al.(1962)Mice(Swiss)leukemia6.71.76.145Fiore-Donatiet al.Table 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-55Ratio of juvenile to adult potencyUnweightedSpeciesgeometric97.5Compound(strain)Sex Dose Tumor Daymean 2.5% Median%Reference5.1 1.14.738 (1962)UrethaneMice (B6AF1/J) male 1 mg/g liver 21 5.1 1.44.730 Klein (1966)(continued)female1mg/g liver 21 0.20.00190.266.0Harderiangland 1 0.3 0.00210.33117 0.3 0.00210.331114 0.6 0.00440.8520male 1 mg/g Harderian gland 210.3 0.00240.4113male1mg/gforestomach 1 0.10.00090.0791.9female 1mg/g forestomach 1 0.4 0.00280.4911male 1mg/g forestomach 7 0.1 0.00170.193.5female 1mg/g forestomach 7 0.1 0.00130.165.0male 1mg/g forestomach 14 0.2 0.00180.213.9female 1mg/g forestomach 14 0.8 0.00561.118male 1mg/g forestomach 21 0.1 0.00080.0721.7female 1mg/g forestomach 21 0.2 0.00150.26.3lung 1 1.0 0.360.952.5male 1mg/glung 14 0.8 0.260.82.3female 1mg/g lung 14 0.4 0.160.451.121 0.9 0.310.862.4Mice (C3H/f) male 1 mg/g liver114 4.01281 Liebelt et al. (1964)female 1mg/g liver 1 16 3.215155male 1mg/g lung 1 5.9 1.75.628female 1mg/g lung 1 22 4.520203male 1 mg/g reticular tissue 12.0 0.0232.338female 1 mg/g reticular tissue 18.6 2.37.760Mice (Swiss)1 mg/g pulmonary2 vs 4 weeks 14 1.110.1965 Rogers(1951)adenomasTable 6. Ratio of early-life to adult cancer potenciesfor studies with acute exposures of juveniles and adultanimals to carcinogens with a mutagenic mode of action (continued)



# A-56CompoundSpecies(strain)SexDoseTumorDayRatio of juvenile to adult potencyReferenceUnweightedgeometricmean2.5%Median97.5%1mg/gpulmonaryadenomas2 vs 6 weeks161.311.31025Urethane(continued)1mg/gpulmonaryadenomas2 vs 8 weeks191.613.311261mg/gpulmonaryadenomas2 vs 10 weeks211.914.511680.25 mg/gadenomas3 vs 8 weeks7.12.36.7290.5 mg/gadenomas3 vs 8 weeks0.70.290.671.61.0 mg/gadenomas3 vs 8 weeks0.70.280.681.6*The 2.5% and 97.5% are percentilesof the posterior distribution. For a Bayesian distribution, thesepercentiles function inamanner 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 with juvenileand adult animals to carcinogens with mutagenic or nonmutagenic modes of action*



# A-57UnweightedgSpecieseometricCompound(strain)SexDoseTumormean2.5%Median97.5%ReferenceMutagenic compoundsDENRats (Colworth)multipleliver2.80.00935.623Peto et al. (1984)esophagus0.180.00150.234.8SafroleMice (B6C3F1)maleliver503.750253Vesselinovitch et al.(1979b)femaleliver4.00.0074.023UrethaneMice (B6AF1/J)male2.5 mg/pupliver790.361021,064Klein (1966)female2.5mg/pupliver0.470.00220.5542Nonmutagenic compoundsDDTMice (B6C3F1)liver230.00230.5823Vesselinovitch et al.(1979a)DieldrinMice (B6C3F1)liver910.0141491Vesselinovitch et al.(1979a)DPHRats (F344/N)male630:800liver0.310.00190.3718Chhabra et al. (1993b)630:2,400liver0.360.00210.4517female630:800liver0.330.00190.3921630:2,400liver0.330.00190.3921Mice(B6C3F1)male210:100liver0.710.00280.9349210:300liver140.0323214female210:200liver0.320.0020.4213210:600liver0.350.00230.538.8ETURats (F344/N)male90:83thyroid0.230.00170.37.3Chhabra et al. (1992)90:250thyroid9.11.110.527female90:83thyroid0.370.00210.461990:250thyroid0.610.00341.110Table 7. Ratio of early-life to adult cancer potencies for studies with lifetime exposures starting with juvenileand adult animals to carcinogens with mutagenic or nonmutagenic modes of action (continued)



# A-58UnweightedSpeciesgeometricCompound(strain)SexDoseTumormean2.5%Median97.5%ReferenceETU(continued)Mice (B6C3F1)male330:330liver0.370.00220.514330:1,000liver0.480.00270.7512female330:330liver0.330.00230.57.8330:1,000liver0.420.00250.6511male330:330thyroid0.440.00220.5234330:1,000thyroid0.630.00351.1210female330:330thyroid5.20.01110108330:1,000thyroid0.180.00160.244.2male330:330pituitary0.400.00210.4732330:1,000pituitary0.180.00150.225.7female330:330pituitary0.210.00160.2610330:1,000pituitary0.270.00190.369.0PBBRats (F344/N)male10:10liver0.390.00230.5613Chhabra et al. (1993a)10:30liver0.180.00160.254.3female10:10liver3615368610:30liver3.10.0234.622male10:10mononuclearcellleukemia0.510.00250.6923male10:30mononuclearcellleukemia0.770.00311.135female10:10mononuclearcellleukemia0.540.00260.7424female10:30mononuclearcellleukemia0.340.00210.4515Mice(B6C3F1)male30:30liver8.90.01512.21,076female30:30liver4.40.00756.2786male10:10liver0.150.00140.23.9Table 7. Ratio of early-life to adult cancer potencies for studies with lifetime exposures starting with juvenileand adult animals to carcinogens with mutagenic or nonmutagenic modes of action (continued)CompoundSpecies(strain)SexDoseTumorUnweightedgeometricmean2.5%Median97.5%Referencefemale10:10liver0.290.00210.437.0*The 2.5% and 97.5% are percentilesof the posterior distribution. For a Bayesian distribution, thesepercentiles function inamanner similar to the 95% confidence limitsfor other types of statistical analyses.



# A-59Table 8. Summary of quantitative estimates of ratio of early-life to adult cancer potencies



# A-60InverseDoseTissueNumber ofchemicalsweightedgeometric meanratioUnweightedMinimumUnweightedMaximumNumber ofratiosPercentage>1Chemicals with mutagenic mode of actionRepeated410.50.121114542Lifetime38.70.1879667Combined repeated and lifetime610.40.121115145AcuteCombined111.50.0117826855Forestomach30.0760.011.93216Harderian20.480.060.8200.0Kidney21.60.177.11878Leukemia15.95.16.72100Liver58.10.10407077Lung71.10.041787756Lymph21.81.12.73100Mammary (wk 5 vs wk 26)17.1NANA1100Mammary (wk 2 vs wk 5–8 or 26)10.071NANA20Nerve22.30.2464875Nerve (Day 1 comparison)2100.2464367Ovarian10.0330.010.1330Reticular tissue16.51.968.62100Thymic lymphoma12.81.017.96100Thyroid10.050.030.0820Uterine/vaginal11.60.038.6367Day 171.70.0117812755Day 1531.50.06527465Chemicals with nonmutagenic mode of actionRepeated62.20.06132227Lifetime53.40.15363821

# Table 9. Excess Relative Risk (ERR) estimates for cancer incidence from

Life Span Study (Japanese survivors) a



# Average ERR at 1 Sv

Site 

# <20 b 

# >20 b



# 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 Study a



# 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 Revi sed Methodology mortality risk model

(from U.S. EPA, 1999) a



# Cancer type Risk model

type b 

# Age group

0–9 10–19 20–29 30–39 40+

Male:

Stomach R 1.223 1.972 2.044 0.3024 0.2745

Colon R 2.290 2.290 0.2787 0.4395 0.08881

Liver R 0.9877 0.9877 0.9877 0.9877 0.9877

Lung R 0.4480 0.4480 0.0435 0.1315 0.1680

Bone A 0.09387 0.09387 0.09387 0.09387 0.09387

Skin A 0.06597 0.06597 0.06597 0.06597 0.06597

Breast R 0.0 0.0 0.0 0.0 0.0

Ovary R 0.0 0.0 0.0 0.0 0.0

Bladder R 1.037 1.037 1.037 1.037 1.037

Kidney R 0.2938 0.2938 0.2938 0.2938 0.2938

Thyroid A 0.1667 0.1667 0.1667 0.1667 0.1667

Leukemia R 982.3 311.3 416.6 264.4 143.6

Female:

Stomach R 3.581 4.585 4.552 0.6309 0.5424

Colon R 3.265 3.265 0.6183 0.8921 0.1921

Liver R 0.9877 0.9877 0.9877 0.9877 0.9877

Lung R 1.359 1.359 0.1620 0.4396 0.6047

Bone A 0.09387 0.09387 0.09387 0.09387 0.09387

Skin A 0.06597 0.06597 0.06597 0.06597 0.06597

Breast R 0.7000 0.7000 0.3000 0.3000 0.1000

Ovary R 0.7185 0.7185 0.7185 0.7185 0.7185

Bladder R 1.049 1.049 1.049 1.049 1.049

Kidney R 0.2938 0.2938 0.2938 0.2938 0.2938

Thyroid A 0.3333 0.3333 0.1667 0.1667 0.1667

Leukemia R 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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