Carcinogen
Introduction
Cancer is a group of diseases characterized by abnormal cell growth that can invade or spread to other parts of the body.
- These are in contrast to benign tumours, which do not spread.
- Several national and international agencies review available scientific evidence to assess the cancer-causing potential of various substances.
International Agency for Research on Cancer (IARC)
The IARC, established in 1965, is part of the World Health Organization (WHO).
- Since 1971, more than 1000 agents have been evaluated, of which more than500 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 and their corresponding monographs can be found online at the following links:
- Classifications: https://monographs.iarc.who.int/agents-classified-by-the-iarc/
- Monographs: 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
The tenth revised edition of the GHS (GHS Rev.10) published in 2023, is the most recent revised edition available.
- Following the 2-year cycle of work of the GHS Sub-Committee of Experts, a new revised edition of the GHS may be expected to be published in 2025.
National Toxicology Program (NTP)
The NTP, an interagency group coordinated by the U.S. Department of Health and Human Services, publishes the Report on Carcinogens (RoC).
The 15th RoC includes 256 listings of substances - chemical, physical, and biological agents; mixtures; and exposure circumstances - that are known or reasonably anticipated to cause cancer in humans.
- The substances are listed either as "known to be human carcinogen" or "reasonably anticipated to be a human carcinogen".
Summary
Several 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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