National Toxicology Program

National Toxicology Program

Questions and Answers about the RoC

What is the Report on Carcinogens (RoC)?

The RoC is a congressionally mandated, science-based public health document prepared by the National Toxicology Program (NTP) that identifies substances, mixtures of chemicals, or exposure circumstances (collectively called substances) that pose a cancer hazard to people living in the United States. The listings in the RoC identify substances as known or reasonably anticipated to be human carcinogens and include a wide range of substances, including metals, pesticides, drugs, fibers, biologicals and chemicals.

Each edition of the report is cumulative and consists of substances newly reviewed in addition to those listed in previous editions. For each listed substance, the RoC contains a substance profile, which provides information from cancer studies that support the listing as well as information about potential sources of exposure and current Federal regulations to limit exposures.

The National Toxicology Program (NTP) prepares the draft RoC on behalf of the Secretary, HHS. The most recent report, the 12th RoC, was published in 2011.

What is the legislation that mandates the RoC?

The RoC was mandated in 1978 (see Section 301 (b)(4) of the Public Health Service Act, as amended)[1] which stipulates that the Secretary, Health and Human Services shall publish a biennial report which contains:
A. A list of all substances (i) which either are known to be carcinogens [in humans] or may reasonably be anticipated to be [human] carcinogens; and (ii) to which a significant number of persons residing in the United States are exposed;
B. Information concerning the nature of such exposure and the estimated number of persons exposed to such substances;
C. A statement identifying (i) each substance contained in this list for which no effluent, ambient, or exposure standard has been established by a Federal agency; and (ii) 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, on the basis of available medical, scientific, or other data, such standard, and the implementation of such standard by the agency, decreases the risk to public health from exposure to the substance;
D. A description of (i) each request received during the year to conduct research into, or testing for, the carcinogenicity of substances and (ii) how the Secretary and each such other entity, respectively, have responded to each request.

How are substances nominated to the RoC?

Anyone can nominate a substance to the NTP for consideration of its listing in, or removal from, the RoC. Nominations come from individuals, or on behalf of non-profit, commercial, governmental or other organizations. The NTP encourages the broadest participation from interested individuals or parties in nominating agents, substances, mixtures or exposure circumstances for listing in or delisting from the RoC. For more information on the process, or to make a nomination to the RoC, see Call for Nominations.

How are nominations evaluated for listing in the RoC?

The NTP initially evaluates each nomination to determine whether the scientific information available for a nomination justifies its formal review and consideration. The NTP announces nominations proposed for review and solicits public comments through announcements in the Federal Register and NTP publications. The evaluation of nominations for listing in the RoC is a formal, multi-step process with multiple opportunities for public comment and is performed by scientists from the NTP, other Federal health research and regulatory agencies, and non-government institutions (see Review Process).

A background document, summarizing information on human exposure, cancer studies in humans and experimental animals, studies on genetic effects and potential cancer mechanisms, is written for each substance and is used in the review process. Final background documents are available via the RoC web page Documents and Reviews.

How are substances defined that cause or might cause cancer in humans?

Agents, substances, mixtures, or exposures (collectively called substances) can be listed in the RoC, either as known to be a human carcinogen or as reasonably anticipated to be a human carcinogen. General descriptions of these two categories are given below.

Known to be a Human Carcinogen

This category is used primarily when there is sufficient evidence of cancer from human studies showing a cause-and-effect relationship between exposure to the substance and human cancer. Occasionally, substances are listed in this category based on human studies showing that the substance causes biological effects known to lead to the development of cancer.

Reasonably Anticipated to be a Human Carcinogen

This category includes substances for which there is limited evidence of cancer in humans or sufficient evidence of cancer in experimental animals showing a cause-and-effect relationship between exposure to the substance and cancer. Alternatively, a substance can be listed in this category if there is evidence that it is a member of a class of substances already listed in the RoC or causes biological effects known to lead to the development of cancer.

Conclusions regarding carcinogenicity in humans or experimental animals are based on expert, scientific judgment, with consideration given to all relevant information (see formal, specific listing criteria).

What does a listing in the RoC mean?

Because nearly everyone is concerned about the relationship between their environment and cancer, the RoC can help inform the public about potential cancer hazards. A listing in the RoC does not by itself establish that a substance will cause cancer in an individual. Many factors, including the amount and duration of an exposure, and an individuals susceptibility to a substance, impact whether a person will develop cancer or not. Formal risk assessments, that take into account these factors, are the purview of the appropriate federal, state, and local health regulatory and research agencies.

The RoC is meant to be a science-based, authoritative public health communication tool, not a regulatory document; however, it provides important information to congressional staff, regulatory agencies, and others who can use it to make informed decisions that protect the health of people in the United States. Certain federal and state agencies have chosen to base some regulatory actions on the listing of a substance in the RoC, considering it an authoritative source regarding the identification of carcinogens or potential carcinogens for hazard communication purposes. For example,

Under the Toxic Substances Control Act, the EPAs Criteria for the Evaluation of Permit Applications for Ocean Dumping of Materials (Title 40, Section 227.6(5)) is a regulation which prohibits ocean dumping of materials considered by responsible scientific opinion to contain known or suspect carcinogens, mutagens, or teratogens, as other than trace contaminants.

The OSHA Hazard Communication Standard requires employers to establish hazard communication programs to transmit information on the hazards of chemicals to their employees by means of labels on containers, material safety data sheets, and training programs.

California's Safe Drinking Water and Toxic Enforcement Act of 1986 initiative, or Proposition 65, is intended to protect California citizens and the State's drinking water sources from chemicals known to cause cancer, birth defects or other reproductive harm, and to inform citizens about exposures to such chemicals. Substances identified in the RoC may be placed on the Prop 65 list, thus influencing the labeling of certain products in California and nationwide.

How many RoCs have been published?

To date, twelve editions of the RoCs have been published; each is cumulative and replaces all previous editions. The first RoC was published in 1980 and the most recent, the 12th RoC, was published in 2011 and contains 240 listings, some of which consist of classes of structurally related chemicals or agents.


1The original requirement for this report was established in November 1978 by the Community Mental Health Center Act, Amendments, Section 262, Public Law 95-622, Part E (pp. 3435-3436). An amendment in 1993 (42 US Code 241) substituted a biennial report for an annual report in the introductory provisions.

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The NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.