National Toxicology Program

What is the Report on Carcinogens (RoC)?

The RoC is a congressionally mandated document prepared by the NTP for the purpose of identifying substances, mixtures of chemicals, or exposure circumstances associated with technological processes that cause or might cause cancer and to which a significant number of persons in the United States are exposed. Listed in the RoC are a wide range of substances, including metals, pesticides, drugs, and natural and synthetic chemicals.

The RoC is an informational scientific and public health document. It serves as a meaningful and useful compilation of data on (1) the carcinogenicity, genotoxicity, and biologic mechanisms of the listings in humans and/or in animals, (2) the potential for human exposure, and (3) current Federal regulations to limit exposures.

The evaluation of nominations for listing in the RoC is performed by scientists from the NTP, other Federal health research and regulatory agencies, and non government institutions. The listings in the RoC identify a substance or exposure circumstance as a known or reasonably anticipated human carcinogen. The RoC is a hazard identification document and does not present quantitative assessments of the risks of cancer associated with exposure to these substances. Thus a listing in the RoC only indicates a potential hazard and does not estimate cancer risks to individuals associated with exposures in their daily lives.

What is the legislation that mandated the RoC?

The RoC is mandated by Section 301 (b) (4) of the Public Health Services Act, as amended, which stipulates that the Secretary of the Department of Health and Human Services shall publish an annual report, which contains:

1. 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;
   
2. Information concerning the nature of such exposure and the estimated number of persons exposed to such substances;
   
3. 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;
   
4. 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.

In 1993 Public Law 95-622 was amended to change the frequency of publication from an annual to a biennial report.

How many RoCs have been published?

To date, 11 RoCs have been published; the 11th RoC contains 246 entries. The 12th RoC is currently under review.

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

Agents, substances, or exposure circumstances are listed as either "known to be a human carcinogen," or "reasonably anticipated to be a human carcinogen." The category "known to be a human carcinogen" is reserved for those substances for which there is sufficient evidence of carcinogenicity from studies in humans that indicates a causal relationship between exposure to the agent, substance, or mixture and human cancer." The second category, "reasonably anticipated to be a human carcinogen" includes those substances for which there is limited evidence of carcinogenicity in humans and/or sufficient evidence of carcinogenicity in experimental animals. Conclusions regarding carcinogenicity in humans or experimental animals are based on scientific judgment, with consideration given to all relevant information. ( See Listing Criteria)

What does a listing in the RoC mean?

The RoCs are informational (not regulatory) scientific and public health documents that serve to inform and educate the public and health care professionals of the risk of exposure to carcinogens by providing 1) available cancer data in humans and/or animals for the substance of interest; 2) the potential for exposure to the substances listed, and 3) the regulations promulgated by Federal agencies to limit exposures. It is important to note that the reports do not present quantitative assessments of carcinogenic risk, nor do they address any potential benefits of exposures to listed substances such as certain pharmaceuticals. Listing in the report does not establish that such substances present a risk to persons in their daily lives. Such formal risk assessments are the purview of the appropriate federal, state, and local health regulatory and research agencies.

The listing of a substance in the RoC is not in itself a regulatory action, but listing may prompt regulatory agencies to consider limiting exposures or uses of a substance. Examples of such actions would include the following:

The OSHA Hazard communication standard states that "Chemical manufacturers and importers shall evaluate chemicals produced in their workplaces or imported by them to determine if they are hazardous. . . and that chemical manufacturers, importers and employers evaluating chemicals shall treat the NTP Annual RoC as a source establishing that a chemical is a carcinogen or potential carcinogen for hazard communication purposes." Written hazard communications required of employers for carcinogens include labels and other forms of warning, material safety data sheets, and employee information and training.

California's Safe Drinking Water and Toxic Enforcement Act of 1986 initiative, or Proposition 65, requires "clear and reasonable warnings" for "knowing and intentional exposures" to chemicals that have been placed on the Proposition 65 list of substances known to cause cancer or reproductive toxicity. The NTP has been designated as authoritative in the area of carcinogenicity, and, chemicals identified in the RoC may be placed on the Proposition 65 list and influence the labeling of certain products containing such substances nationwide.