Report on

Carcinogens

2014

th

U.S. Department of Health and Human Services

Public Health Service

National Toxicology Program

Pursuant to Section 301 (b) (4) of the Public Health 

Service Act as amended by Section 262, PL 95-622
Report on Carcinogens, Thirteenth Edition

National Toxicology Program, Department of Health and Human Services

For Table of Contents, see home page: http://ntp.niehs.nih.gov/go/roc13

Introduction

The probability that a resident of the United States will develop cancer at some point in his or her lifetime is approximately 1 in 2 for men 

and 1 in 3 for women (ACS 2014). Nearly everyone’s life has been directly or indirectly affected by cancer. Most scientists involved in cancer research believe that the environment in which we live and work 

may be a major contributor to the development of cancer (Reuben 

2010). In this context, the “environment” is anything that people interact with, including exposures resulting from lifestyle choices, such 

as what we eat, drink, or smoke; natural and medical radiation, including exposure to sunlight; workplace exposures; drugs; socioeconomic factors that affect exposures and susceptibility; and substances 

in air, water, and soil (OTA 1981, Hanna and Coussens 2001). Other 

factors that play a major role in cancer development are infectious 

diseases, aging, and individual susceptibility, such as genetic predisposition (Montesano and Hall 2001). Many experts firmly believe 

that much of the cancer associated with the environment may be 

avoided (Reuben 2010). 

The people of the United States, concerned about the relationship 

between their environment and cancer, have asked, through the U.S. 

Congress, for information about substances that are known or appear likely to cause cancer (i.e., to be carcinogenic). Section 301(b)(4) 

of the Public Health Service Act, as amended, requires that the Secretary of the Department of Health and Human Services (DHHS) 

publish a biennial report that contains the following information: 

• A list of all substances (1) which either are known to be 

human carcinogens or may reasonably be anticipated to be 

human carcinogens and (2) to which a significant number of 

persons residing in the United States are exposed.

• Information concerning the nature of such exposure and the 

estimated number of persons exposed to such substances. 

• A statement identifying (1) each substance contained in this 

list for which no effluent, ambient, or exposure standard has 

been established by a Federal agency and (2) for each effluent, 

ambient, or exposure standard established by a Federal agency 

with respect to a substance contained in this list, the extent to 

which such standard decreases the risk to public health from 

exposure to the substance. 

• A description of (1) each request received during the year to 

conduct research into, or testing for, the carcinogenicity of a 

substance and (2) how the Secretary and other responsible 

entities responded to each request. 

The Report on Carcinogens (RoC) is an informational scientific and 

public health document that identifies and discusses agents, substances, mixtures, or exposure circumstances (hereinafter referred to 

as “substances”) that may pose a cancer hazard to humans. For each 

listed substance, the RoC contains a substance profile which provides 

information on (1) the listing status, (2) cancer studies in humans 

and animals, and often studies of biologic mechanisms and other 

data relevant to carcinogenicity, (3) the potential for human exposure 

to these substances, and (4) Federal regulations to limit exposures. 

The substances listed in the RoC are either known or reasonably 

anticipated to cause cancer in humans in certain situations. A listing in the RoC does not by itself establish that a substance will cause 

cancer in an individual. Many factors, including the intrinsic carcinogenicity of the substance, the amount and duration of exposure, and 

the individual’s susceptibility to the carcinogenic action of the substance, affect whether a person will or will not develop cancer. The 

RoC does not attempt to rank substances according to the relative 

cancer hazards they pose or present quantitative assessments of the 

risks of cancer associated with these substances. Such formal risk assessments are the responsibility of the appropriate Federal, state, and 

local health regulatory and research agencies.

As stated above, the purpose of the RoC is to identify cancer hazards to human health; therefore, it is not within the scope of this report to address potential benefits of exposure to certain carcinogenic 

substances in special situations. For example, numerous drugs typically used to treat cancer or other medical conditions have been 

shown to increase the frequency of primary cancer (i.e., cancer located in the organ or tissue where it originated) or secondary cancer (i.e., cancer that has spread from its organ or tissue of origin to 

other parts of the body) in patients undergoing treatment for specific diseases. In these cases, the benefits of using the drug to treat or 

prevent a specific disease may outweigh the added cancer risk associated with its use. Personal decisions concerning voluntary exposure 

to carcinogenic substances should be made only after consultation 

with a physician or other appropriate specialist, and not based solely 

on the information contained in the RoC. 

Identification of Carcinogens

For many years, government research agencies (including the National Toxicology Program), industries, academia, and other research 

organizations have studied various substances to identify those that 

may cause cancer. Much of the information on specific chemicals or 

occupational exposures has been published in the scientific literature 

or in publicly available and peer-reviewed technical reports. This literature is a primary source of information for identifying and evaluating substances for listing in the RoC. Many of the listed substances 

also have been reviewed and evaluated by other organizations, including the World Health Organization’s International Agency for 

Research on Cancer (IARC), in Lyon, France, and other international 

agencies, as well as the Environmental Protection Agency of the State 

of California and U.S. federal agencies, such as the U.S. Environmental Protection Agency. 

Studies in both humans and experimental animals are used to 

evaluate whether substances are potentially carcinogenic in humans. 

Other studies that may elucidate possible mechanisms of action of 

potential carcinogens also are considered in the evaluations. The 

strongest evidence for establishing a relationship between exposure 

to any given substance and cancer in humans comes from epidemiological studies — studies of the occurrence of a disease in a defined 

human population and the factors that affect its occurrence (Hill 

1971). Interpretation of epidemiological studies of human exposure 

and cancer can be difficult, as they must rely on natural, not experimental, human exposure and must therefore consider many factors 

that may affect cancer incidence in addition to the exposure under 

study (Rothman et al. 2012). One such factor is the latency period for 

cancer development (i.e., the time between first exposure to a carcinogen and development of cancer). The first sign of cancer often 

appears many years (sometimes 20 to 30 years or more) after exposure to the carcinogen. Epidemiological studies of workers exposed 

to high levels of chemicals have led to the identification of many carcinogens in the United States (Fontham et al. 2009).

Another valuable method for identifying substances as potential 

human carcinogens is the long-term bioassay in experimental animals. These studies provide accurate information about dose and 

duration of exposure, and they are less affected than epidemiological studies by possible interactions of the test substance with other 

chemicals or modifying factors (Huff 1999). Experimental cancer research is based on the scientific assumption that substances causing 

cancer in animals will have similar effects in humans; however, it is 

not possible to predict with complete certainty from animal stud-
Report on Carcinogens, Thirteenth Edition

National Toxicology Program, Department of Health and Human Services 2

ies alone which substances will be carcinogenic in humans. Known 

human carcinogens have also been shown to cause cancer in experimental animals when tested adequately (Fung et al. 1995). In many 

cases, a substance first was found to cause cancer in animals and later 

confirmed to cause cancer in humans (Huff 1993, 1999). How experimental animals respond to substances, including developing cancer 

or other illnesses, does not always strictly correspond to how people will respond. Nevertheless, experimental animal studies remain 

a valuable tool for detecting potential human health hazards of all 

kinds, including cancer (OTA 1981, Tomatis et al. 1997). 

In addition to the use of studies in humans and experimental animals, alternative testing methods that incorporate advances in molecular toxicology, computational sciences, and information technology 

are being developed to prioritize substances for carcinogenicity testing and reduce the use of animals in testing. A 2007 report by the 

National Academy of Science’s National Research Council, Toxicity 

Testing in the 21st Century (NRC 2007), outlined strategies for new 

approaches, and a research collaboration among the National Toxicology Program (NTP), the U.S. Environmental Protection Agency 

(EPA), the National Center for Advancing Translational Sciences, 

and the U.S. Food and Drug Administration (FDA) was established 

to evaluate whether high-throughput/high-content in vitro screening assays, alternative animal models using, for example, zebrafish 

(Danio rerio) and the roundworm Caenorhabditis elegans, and computational toxicology approaches can be used initially to facilitate prioritization of chemicals for further testing and ultimately to enable 

more effective predictions of carcinogenic risk of substances to humans (Collins et al. 2008).

Preparation of the RoC

The NTP prepares the RoC on behalf of the Secretary of Health and 

Human Services. For the preparation of the Thirteenth Report on Carcinogens, the NTP followed a four-part process (http://ntp.niehs.nih.

gov/go/rocprocess) using established criteria (see Listing Criteria, below). New to the process for the Thirteenth Report on Carcinogens is 

the preparation of an RoC Monograph for each substance selected 

for review for the RoC. The process provides numerous opportunities for public comment, input from external scientists and government scientists, and peer review of the scientific information. Details 

of the process are described in the section of the RoC entitled Process for Preparation of the Report on Carcinogens.

Listing Criteria

The criteria for listing an agent, substance, mixture, or exposure circumstance in the RoC are shown in the box on this page. The listing 

criteria presented here were first adopted for use in the Eighth Report on Carcinogens, which was published in 1998. The listing criteria were clarified the following year in two Federal Register notices 

(NTP 1999a,b). Listing criteria for substances listed in earlier editions of the RoC are outlined in the introductions to those editions. 

Estimation of Exposure 

The RoC is required to list only substances to which a significant 

number of people living in the United States are exposed. Some substances that have been banned or restricted in use (e.g., safrole, arsenical pesticides, and mirex) are listed either because people who 

were previously exposed remain potentially at risk or because these 

substances still are present in the environment. 

The RoC is also required to provide information about the nature of exposures and the estimated numbers of people exposed to 

listed substances. Because little information typically is available, estimating the number of people who could be exposed and the route, 

intensity, and duration of exposure for each substance is a difficult 

task. However, other types of information, such as data on use, production, occupational exposure, and exposure from environmental 

release or occurrence, can be used to determine whether there is 

(or was) exposure in the United States, and this information is included in each substance profile. The National Institute for Occupational Safety and Health (NIOSH) has conducted two occupational 

exposure surveys: the National Occupational Hazard Survey (NOHS), 

conducted from 1972 to 1974, and the National Occupational Exposure Survey (NOES), conducted from 1981 to 1983. These surveys yielded data on potential exposure to many listed substances. 

Although dated, NOES estimates are provided in the profiles of the 

listings when available, and NOHS figures are provided if no other 

exposure data are available.

Known To Be Human Carcinogen: 

There is sufficient evidence of carcinogenicity from studies in 

humans,* which indicates a causal relationship between exposure to the agent, substance, or mixture, and human cancer. 

Reasonably Anticipated To Be Human Carcinogen: 

There is limited evidence of carcinogenicity from studies in 

humans,* which indicates that causal interpretation is credible, but that alternative explanations, such as chance, bias, 

or confounding factors, could not adequately be excluded, 

or 

there is sufficient evidence of carcinogenicity from studies in 

experimental animals, which indicates there is an increased 

incidence of malignant and/or a combination of malignant 

and benign tumors (1) in multiple species or at multiple tissue sites, or (2) by multiple routes of exposure, or (3) to an 

unusual degree with regard to incidence, site, or type of tumor, or age at onset, 

or 

there is less than sufficient evidence of carcinogenicity in humans or laboratory animals; however, the agent, substance, or 

mixture belongs to a well-defined, structurally related class 

of substances whose members are listed in a previous Report on Carcinogens as either known to be a human carcinogen or reasonably anticipated to be a human carcinogen, or 

there is convincing relevant information that the agent acts 

through mechanisms indicating it would likely cause cancer in humans. 

Conclusions regarding carcinogenicity in humans or experimental animals are based on scientific judgment, with consideration given to all relevant information. Relevant information 

includes, but is not limited to, dose response, route of exposure, 

chemical structure, metabolism, pharmacokinetics, sensitive 

sub-populations, genetic effects, or other data relating to mechanism of action or factors that may be unique to a given substance. For example, there may be substances for which there is 

evidence of carcinogenicity in laboratory animals, but there are 

compelling data indicating that the agent acts through mechanisms which do not operate in humans and would therefore not 

reasonably be anticipated to cause cancer in humans.

*This evidence can include traditional cancer epidemiology studies, data from clinical studies, and/or data derived from the study of tissues or cells from humans 

exposed to the substance in question, which can be useful for evaluating whether 

a relevant cancer mechanism is operating in humans.
Report on Carcinogens, Thirteenth Edition

National Toxicology Program, Department of Health and Human Services 3

Regulations and Guidelines 

The RoC is required to identify each of the listed substances for which 

no standard for exposure or release into the environment has been 

established by a Federal agency. The RoC addresses this requirement 

by providing in each profile a summary of the regulations and guidelines, if any, that are likely to decrease human exposure to that substance. Some of these regulations and guidelines have been enacted 

for reasons other than the substance’s carcinogenicity (e.g., to prevent adverse health effects other than cancer or to prevent accidental 

poisoning of children). These regulations are included in the profiles 

because reduction of exposure to a suspected or known carcinogen 

is likely to reduce the risk for cancer. Regulations are organized by 

regulatory agencies and the acts enforced by those agencies, and are 

provided at the end of each profile. 

Four of the agencies participating with the NTP in preparation of 

the Thirteenth Report on Carcinogens—the Consumer Product Safety 

Commission (CPSC), EPA, FDA, and Occupational Safety and Health 

Administration (OSHA)—are responsible for regulating hazardous 

substances and limiting the exposure to and use of such substances, 

and the majority of the regulations cited in the RoC were enacted by 

those agencies. The guidelines cited in the RoC are primarily those 

published by NIOSH and the American Conference of Governmental Industrial Hygienists. In addition, regulations and guidelines enacted by other governmental agencies are cited if their likely outcome 

is to reduce exposure to the substance. It is beyond the scope of this 

report to provide detailed information or interpretation concerning 

the implementation of each regulatory act, and no attempt is made 

to do so. Some commonly used regulatory terms are defined in the 

Glossary, which follows the Substance Profiles. Links to the Web sites 

for the Code of Federal Regulations and for each of the major regulatory agencies are provided at the end of the Reference section of this 

Introduction for those wishing to obtain additional information on 

these agencies and their regulations. 

An OSHA regulation identified in some of the listing profiles requires clarification. Specific substances are listed as having “comprehensive standards” if, in addition to the permissible exposure limit 

(PEL), OSHA has regulations for the substance that include provisions for exposure monitoring, engineering and work practice controls, use of respirators and protective garments and equipment, 

hygiene facilities, information and training, labeling of substance 

containers and worker areas in which the substance is used, and 

health screening programs. The sets of comprehensive standards are 

provided in 29 CFR 1910 Subpart Z and also on the OSHA Web site.

Some specific regulatory actions may depend on the listing of a 

substance in the RoC. Information on three such actions, which potentially apply to all or a substantial subset of the listing of substances 

in the RoC, are not identified individually in the listing profiles, but 

are described below. Two regulations—the OSHA Hazard Communication Standard and the EPA Criteria related to ocean dumping—apply or potentially apply to all substances listed in the RoC, because 

that is one of several criteria that may be used to classify a substance 

as a carcinogen according to the regulations. The third regulation, 

under the Toxic Substances Control Act (TSCA), applies to certain 

listed substances because its application depends on both listing in 

the RoC and in one of several specific lists of chemicals distributed 

in commerce or meeting other specifications as defined by TSCA.

• OSHA’s Hazard Communication Standard. This regulation 

is intended to communicate the hazards of chemicals and 

appropriate protective measures to protect employees. In 

2012, OSHA modified this standard to conform to the United 

Nations’ Globally Harmonized System of Classification 

and Labelling of Chemicals (GHS). The program includes 

maintenance of a list of hazardous chemicals, labeling 

of shipped and workplace containers, preparation and 

distribution of safety data sheets to employees, and provision 

of employee training. The rule states that a chemical may be 

considered a carcinogen or potential carcinogen for hazard 

communication purposes in lieu of applying the classification 

criteria described in the standard if it has been listed as 

a carcinogen or potential carcinogen in current editions 

of (1) the RoC, (2) the IARC monographs, or (3) OSHA’s 

Occupational Safety and Health Standards, Subpart Z–Toxic 

and Hazardous Substances.

• EPA’s Criteria for the Evaluation of Permit Applications for 

Ocean Dumping of Materials under the Toxic Substances 

Control Act. This regulation prohibits ocean dumping 

of materials containing “known carcinogens, mutagens, 

or teratogens or materials suspected to be carcinogens, 

mutagens, or teratogens by responsible scientific opinion” as 

other than trace contaminants. 

• TSCA Section 12(b) export notification requirements apply 

to those chemicals listed in the RoC that may be distributed 

in commerce, manufactured, processed, used, or disposed 

of. Section 12(b) of TSCA requires any person exporting 

or intending to export to a foreign country a chemical for 

which data submission is required under TSCA sections 4, 5, 

6, or 7 to notify the EPA Administrator of such exportation 

or intent to export (for more information, see http://www.

epw.senate.gov/tsca.pdf). The RoC is used to evaluate 

eligibility for exemptions from these requirements based 

on de minimis concentration levels. Chemicals listed as 

a carcinogen or potential carcinogen in current editions 

of (1) the RoC, (2) the IARC monographs, or (3) OSHA’s 

Occupational Safety and Health Standards, Subpart Z – Toxic 

and Hazardous Substances are not subject to TSCA section 

12(b) export notification requirements where such chemicals 

are present in a concentration of less than 0.1% by weight 

or volume; however, the de minimis concentration level for 

polychlorinated biphenyls (PCBs) is 50 ppm (for further 

details see http://www.gpo.gov/fdsys/granule/FR-2006-11-

14/E6-19182 and select Text or PDF from Formats under 

Download Files).

Cancer Rates and Estimates of Risk Reduction

Cancer is the second leading cause of death in the United States. 

According to estimates from the American Cancer Society, over 

1.6 million new cancer cases and over 580,000 deaths from cancer 

in the United States are expected to occur in 2014 (ACS 2014). In 

men, the most common sites of newly diagnosed cancer are the prostate, lung and bronchus, and colorectum (colon and rectum); these 

three sites account for 49% of all cancer cases, and prostate cancer 

is the most common (27%). In women, the three most common sites, 

accounting for 50% of the total, are the breast (29%), lung and bronchus, and colorectum. At present, cancer at these sites also results 

in the highest death rates: in men, mortality is highest for cancer of 

the lung and bronchus, followed by the prostate and colorectum; in 

women, mortality is highest for cancer of lung and bronchus, followed by the breast and colorectum (ACS 2014). Data on cancer incidence and death rates were reported in the Annual Report to the 

Nation on the Status of Cancer, 1975–2010 (Edwards et al. 2014) and 

the Cancer Statistics report prepared annually by the American Cancer Society (ACS 2014); both reports use the most recent data from 
Report on Carcinogens, Thirteenth Edition

National Toxicology Program, Department of Health and Human Services 4

the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute (Howlader et al. 2014).

In recent years, overall cancer incidence rates were stable in 

women from 2006 to 2010 (Siegel et al. 2014), while those in men 

decreased modestly (0.6% per year). These decreases are largely explained by decreased rates of colorectal, prostate, and lung cancer 

in men. Declines in colorectal cancer rates were similar in women, 

but the rates for breast cancer were stable from 2006 to 2010, the 

most recent period for which data were available (ACS 2014). Lung 

cancer rates declined more rapidly in men than in women, but decreases were observed for women aged 35 to 44 years and 54 to 64 

years (Henley et al. 2014). Mortality from lung cancer in women decreased by 9% from 2002 to 2010 (Siegel et al. 2014). While decreases 

in overall cancer mortality have been driven by declining death rates 

for the four major cancer sites for each sex, mortality from other types 

of cancers has been increasing. Trend analysis for the period from 

2001 to 2010 showed increasing death rates for cancers of the oropharynx, anus, liver, pancreas, and soft tissue (including the heart) in 

men and women and for melanoma in men. Incidence rates increased 

from 2006 to 2010 for melanoma of the skin, esophageal adenocarcinoma, and cancers of the thyroid, liver, kidney, anus, and pancreas in 

both men and women, with the largest increases for cancers of the 

thyroid and liver (Siegel et al. 2014). 

Of particular concern is that incidence rates of cancer in children 

in the United States increased at a rate of 0.6% per year from 1975 to 

2010 (ACS 2014). For 2014, the American Cancer Society estimated 

that there would be 10,450 new cancer cases in children under the age 

of 14 (all races combined) and 5,330 new cases in those aged 15 to 19. 

The most common cancers in children under 14 are acute lymphocytic leukemia (26%), brain and central nervous system (CNS) cancers (21%), neuroblastoma (7%), and non-Hodgkin lymphoma (6%), 

while those in children aged 15 to 19 are Hodgkin lymphoma (15%), 

thyroid carcinoma (11%), brain and CNS cancers (10%), and testicular germ-cell tumors (8%). Children are particularly vulnerable to 

environmental risk factors, including numerous toxins and detrimental exposures from air, food, water, medicines, pesticides, and ionizing radiation, even before birth (NCI 2010). Despite the increases 

in incidence rates, death rates for childhood and adolescent cancers 

declined steadily from 1975 to 2010, by an average of 2.1% per year.

Cancer also has a major economic impact on American society. 

The costs to American society were estimated by the National Institutes of Health (NIH) to be $99 billion for direct medical costs 

in 2009, and these costs more than double if the costs for lost productivity due to illness (estimated at $19.6 billion) and to premature death (estimated at $124.8 billion) are included (Reuben 2010). 

The financial burden resulting from cancer is expected to increase 

further. The NIH (2013) projects direct cancer care expenditures of 

$158 billion in 2020 based on current healthcare costs. If medical 

costs increase, the financial burden of cancer will be even higher, an 

estimated $207 billion in 2020, based on a 5% annual increase in costs. 

IARC has predicted that within two decades, cancer deaths worldwide will increase from 8.2 million (in 2012) to 13 million per year, 

while new cancer cases increase from approximately 14 million to 

22 million per year (Stewart and Wild 2014). However, IARC estimated that between one third and one half of all cancer deaths could 

be prevented by changing behaviors such as reducing use of tobacco, 

avoiding excessive alcohol consumption, protecting against sunburn, 

increasing physical activity, and controlling body weight. IARC also 

noted that reducing exposure to environmental pollution in the water 

and air by regulatory action and technological improvements would 

help to reduce the burden of cancer worldwide. IARC expects the 

future increase in cancer burden to have its greatest impact in lowand middle-income countries, where some cancers, such as those of 

the cervix and liver, are already common, and cancer at other sites 

will increase as a result of demographic changes, as both life expectancy and overall population increase. The cancer profiles of these 

populations also are expected to change as the populations adopt behavioral and lifestyle habits typical of more affluent, industrialized 

countries, likely resulting in increases in female breast cancer, prostate cancer, and colorectal cancer.

Approaches to reduction of cancer incidence and mortality include 

both primary prevention, including the reduction or elimination of 

exposure, and secondary prevention, including early detection via 

screening and treatment of any diagnosed precancerous conditions 

or early malignancies (Bode and Dong 2009). Reduction of tobacco 

use over the past 50 years is largely responsible for the decrease in 

lung-cancer mortality in men. About 40% of the decrease in overall 

cancer mortality in men is due to decreased lung-cancer mortality, 

indicating that primary prevention has a major impact in improving 

public health (Siegel et al. 2014). For example, a combination of education and social policies, such as excise taxes and smoke-free air 

laws, contribute to reducing tobacco use. Mortality from lung cancer has decreased more slowly in women because cigarette smoking 

in women peaked 20 years later than in men. Decreases in mortality 

from cervical, breast, and colon cancer are thought to have resulted 

from a combination of early detection and improvements in treatment, although reduction in the use of menopausal hormone therapy among post-menopausal women starting in 2001 may also have 

contributed to decreases in breast-cancer incidence. 

Primary prevention is the basis of current regulatory policies 

that aim to lower human exposure to cancer-causing substances and 

thereby improve public health. It is reasonable and prudent to accept 

that reducing exposure for any reason, particularly to substances 

shown to be carcinogenic in experimental animals, will decrease the 

incidence of cancer in humans (Tomatis et al. 1997, Montesano and 

Hall 2001). For each effluent, ambient, or exposure standard established by a Federal agency for a listed substance, the RoC is required 

to state the extent to which, on the basis of available medical, scientific, 

or other data, the implementation of that standard decreases the public’s risk for cancer. This statement requires quantitative information 

on how much protection from cancer the public is afforded by established Federal standards. 

Estimating the extent to which listing a substance in the RoC protects public health is perhaps the most difficult task in preparing the 

RoC. The carcinogenic risk depends on many things, including the intensity, route, and duration of exposure to a carcinogen. People may 

respond differently to similar exposures, depending on their age, sex, 

nutritional status, overall health, genetics, and many other factors. 

Only in a few instances can risk for cancer be estimated with complete 

confidence, and these estimations require studies of long-term human 

exposures and cancer incidence in restricted environments, which 

rarely are available. Nevertheless, there is evidence that regulations 

have led to reductions in exposure to a number of substances listed 

in the RoC and probably have contributed, in part, to the decreases 

in cancer incidence and mortality observed over the past decade. The 

reduction in cancer death rates translates to the prevention of approximately 1,340,040 deaths over the 20-year period from 1990 to 

2010 (Siegel et al. 2014). For example, major environmental pollution prevention acts, such as EPA’s Resource Conservation and Recovery Act, Clean Water Act, and Clean Air Act, were passed in the 

early 1970s. These laws have led to reduced exposure to a number of 

pollutants. Although no analyses were found to determine whether 

these regulations have decreased cancer incidences, analyses have 

shown that they have reduced premature deaths from respiratory 
Report on Carcinogens, Thirteenth Edition

National Toxicology Program, Department of Health and Human Services 5

illnesses and heart attacks (EPA 2010). Studies have shown associations between lung-cancer mortality and air pollution; therefore, it 

seems reasonable that regulations reducing air pollution have also 

reduced cancer risks (Montesano and Hall 2001, Raaschou-Nielsen 

et al. 2010). U.S. workplace levels of many occupational carcinogens 

also have been reduced since the 1970s (Fontham et al. 2009), and 

it therefore is presumed that these reductions have prevented occupationally related cancers. 

Listing of Substances in the Thirteenth Report on 

Carcinogens

Each edition of the RoC is cumulative and includes substances newly 

reviewed in addition to those listed in previous editions. The Thirteenth Report on Carcinogens contains profiles for 243 substances, 

some of which (e.g., Estrogens, Steroidal) consist of a class of structurally related chemicals or agents. These include 56 profiles for substances listed as known to be human carcinogens and 187 profiles for 

substances listed as reasonably anticipated to be human carcinogens. 

Profiles for related exposures, such as exposure to various types of ultraviolet radiation, and selected members of chemical families, such 

as nitroarenes, are often grouped together. There are three new listings and one revised listing. The three newly listed substances, 1-Bromopropane, Cumene, and Pentachlorophenol and By-products of Its 

Synthesis, all are listed as reasonably anticipated to be human carcinogens. o-Toluidine, which was first listed in the Third Annual Report 

on Carcinogens in 1983 as reasonably anticipated to be a human carcinogen, is now listed as known to be a human carcinogen. 

The names of all the substances—agents, substances, mixtures, or 

exposure circumstances—listed in the RoC are given in alphabetical 

order for the two listing categories. Part A identifies the substances 

listed in the RoC as known to be human carcinogens, and Part B identifies those listed as reasonably anticipated to be human carcinogens.

The substance profiles contain (1)  a brief description of each substance, with a summary of the evidence considered key for its carcinogenicity, (2) relevant information on properties, use, production, 

and exposure, and (3) a summary of the regulations and guidelines 

that are likely to decrease exposure to the substance. The profiles include references to scientific literature used to support the listings. 

The substances listed in the RoC do not include all human carcinogens. The RoC lists only those nominated agents, substances, mixtures, or exposure circumstances for which relevant data exist and 

have been reviewed and found to meet the listing criteria defined 

above. As additional substances are nominated, they will be considered and reviewed for possible listing in future editions of the RoC. 

Other Information Provided in the Thirteenth 

Report on Carcinogens 

Following the Substance Profiles, additional information is provided 

about terms that are used frequently in the profiles, including a Glossary, a list of Acronyms and Abbreviations, and Units of Measurement. In addition, the following appendices are provided:

• Appendix A provides a list of manufacturing processes, 

occupations, and exposure circumstances classified by IARC 

as carcinogenic to humans. 

• Appendix B lists the agents, substances, mixtures, or exposure 

circumstances that have been delisted from the RoC. 

• Appendix C lists the agents, substances, mixtures, or exposure 

circumstances that have been reviewed but not recommended 

for listing in the RoC. 

• Appendix D identifies participants who collaborated in 

preparation of the Thirteenth Report on Carcinogens. 

• Appendix E provides a link to a searchable database of 

substances nominated to the NTP for toxicological testing.

• Appendix F is a cross-referenced list of substances and their 

common synonyms or abbreviations.

• Appendix G lists, by Chemical Abstract Service (CAS) 

Registry number, all of the chemicals included in the RoC for 

which CAS Registry numbers were identified.

The Thirteenth Report on Carcinogens was prepared following procedures that maximized the quality, objectivity, utility, and integrity of 

the information contained in the report. Although not anticipated, 

factual errors or omissions in this report may be identified after its 

distribution. If this should happen, these errors or omissions will be 

addressed by the NTP. Where appropriate, corrections will initially 

be posted on the NTP Office of the Report on Carcinogens Web site 

at http://ntp.niehs.nih.gov/go/roc and then made in the next edition of the RoC. 

For more information on the Thirteenth Report on Carcinogens,

visit the NTP Office of the Report on Carcinogens Web site at the link 

provided above or contact Dr. Ruth Lunn, Director, Office of the Report on Carcinogens, National Toxicology Program, MD K2-14, P.O. 

Box 12233, Research Triangle Park, NC 27709; telephone (919) 316-

4637; fax (301) 480-2970; e-mail lunn@niehs.nih.gov. 

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Collins FS, Gray GM, Bucher JR. 2008. Transforming environmental health protection. Science 319(5865): 

906-907. 

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Web Sites 

American Conference of Governmental Industrial Hygienists (ACGIH)

http://www.acgih.org/home.htm 

Code of Federal Regulations (CFR), U.S. Government Printing Office

http://www.gpoaccess.gov/cfr/index.html 

Consumer Product Safety Commission (CPSC)

http://www.cpsc.gov

Department of Transportation (DOT)

http://www.dot.gov

Environmental Protection Agency (EPA)

http://www.epa.gov 

Integrated Risk Information System

http://cfpub.epa.gov/ncea/iris/index.cfm

Food and Drug Administration (FDA)

http://www.fda.gov

Center for Food Safety & Applied Nutrition

http://www.fda.gov/aboutfda/centersoffices/officeoffoods/cfsan/default.htm

International Agency for Research on Cancer (IARC). 

http://www.iarc.fr

Monographs on the Evaluation of Carcinogenic Risks of Chemicals to Humans 

http://monographs.iarc.fr/index.php

National Institute for Occupational Safety and Health (NIOSH)

http://www.cdc.gov/niosh

Pocket Guide to Chemical Hazards

http://www.cdc.gov/niosh/npg

NIOSH Safety and Health Topic – Cancer

http://www.cdc.gov/niosh/topics/cancer

NIOSH Carcinogen List

http://www.cdc.gov/niosh/topics/cancer/npotocca.html

National Toxicology Program (NTP)

http://ntp.niehs.nih.gov

Report on Carcinogens

http://ntp.niehs.nih.gov/go/roc

Occupational Safety and Health Administration (OSHA)

http://www.osha.gov