Carcinogen
Introduction
A carcinogen can be defined as a substance or an exposure that can lead to cancer.
- Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign, which do not spread.
There are several national and international agencies review the available evidence to try to determine the cancer-causing potential of different substances.
International Agency for Research on Cancer (IARC)
The IARC, part of the World Health Organization (WHO), is established in 1965. Since 1971, more than 1000 agents have been evaluated, of which 500 have been identified as carcinogenic, probably carcinogenic or possibly carcinogenic to humans.
The Working Group classifies an agent into one of four categories.
- Group 1: Carcinogenic to humans
- Group 2A: Probably carcinogenic to humans
- Group 2B: Possibly carcinogenic to humans
- Group 3: Not classifiable as to its carcinogenicity in humans
The classifications reflect the strength of the scientific evidence as to whether an agent can cause cancer in humans, but they do not reflect how high the risk of developing cancer is at a given exposure level. The types of exposures, the extent of risk, the people who may be at risk, and the cancer types linked with the agent can be very different across agents. Therefore, comparisons within a category can be misleading
The full lists of IARC classifications can be found online at https://monographs.iarc.who.int/agents-classified-by-the-iarc/. The full monographs are available on the site as well, at https://monographs.iarc.who.int/monographs-available/.
Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) is a United Nations initiative to address classification of chemicals by types of hazard and proposes harmonized hazard communication elements, including labels and safety data sheets.
Based on strength of evidence and additional considerations (weight of evidence), substances are classified to 2 categories by carcinogenicity.
- Category 1: Known or presumed carcinogens
- Category 1A: the placing is largely based on human evidence
- Category 1B: the placing is largely based on animal evidence
- Category 2: Suspected human carcinogens
National Toxicology Program (NTP)
The Report on Carcinogens is prepared by the NTP, an interagency group coordinated by the U.S. Department of Health and Human Services.
Substances that can pose a potential cancer hazard can be listed in the Report on Carcinogens either as
- Known to be a human carcinogen
- Reasonably anticipated to be a human carcinogen
The 15th RoC includes information on 256 substances.
Other Agencies and Groups
Other federal agencies, such as the Environmental Protection Agency (EPA), the CDC’s National Institute for Occupational Safety and Health (NIOSH) and the Food and Drug Administration (FDA), and the National Cancer Institute (NCI) may comment on whether a substance or exposure may cause cancer and/or what levels of exposure to a particular substance might be considered acceptable.
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