The short answer
The Report on Carcinogens is a U.S. government list, updated by the National Toxicology Program, of substances that pose a cancer hazard. It uses two categories: 'known' and 'reasonably anticipated' to be human carcinogens. Like IARC, it identifies hazard, not personal risk.
The Report on Carcinogens (RoC) is a congressionally mandated U.S. list of cancer hazards.
It is prepared by the National Toxicology Program (NTP), based at NIEHS.
It uses two categories: 'known' and 'reasonably anticipated' to be human carcinogens.
The 15th edition (2021) has 256 listings.
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The full explanation.
The U.S. counterpart to IARC
The WHO has its IARC Monographs. The United States has its own respected carcinogen list. It is the Report on Carcinogens (RoC), prepared by the National Toxicology Program (NTP). NTP is an interagency program based at the National Institute of Environmental Health Sciences.
The RoC is required by Congress. It is a cumulative, science-based public health document. It identifies substances, mixtures, and exposures that may pose a cancer hazard to people in the United States.
Two categories
IARC uses four groups. The RoC uses just two categories.
- "Known to be a human carcinogen." There is sufficient evidence from studies in people. That evidence shows a cause-and-effect relationship between the exposure and cancer.
- "Reasonably anticipated to be a human carcinogen." There is limited evidence in humans, or sufficient evidence in animals. Strong mechanistic grounds can also support this listing.
The 15th edition (2021) contains 256 listings. Of those, 64 are "known" and 192 are "reasonably anticipated."
Hazard, not risk — again
Just like IARC, the RoC performs hazard identification. A listing means the substance can pose a cancer hazard. It does not mean any one exposure will cause cancer in a given person. The NTP is careful to make this distinction. Real-world risk depends on how much, how often, and how long a person is exposed.
What's new in the latest edition
The 15th edition (2021) added eight new listings. They give a sense of how the process works.
- Chronic Helicobacter pylori infection is the only new "known" carcinogen. It is linked to stomach cancer.
- Antimony trioxide is listed as "reasonably anticipated."
- Six haloacetic acids are byproducts of disinfecting drinking water. All six are "reasonably anticipated."
How it compares to IARC
The RoC and IARC usually reach similar conclusions. But they are separate systems, with different scopes and category labels.
- The RoC is U.S. federal, with two categories.
- IARC is international (WHO), with four groups.
An agent can appear on both lists. Both identify hazard, so the same hazard-versus-risk reasoning applies to each. A listing tells you the evidence is strong enough to flag a cancer hazard. It does not tell you how much risk you personally face.
Why it's useful
The RoC is a trustworthy, government-vetted reference. It shows whether a substance is recognized as a cancer hazard in the United States. Pair it with real-world exposure information, and with an EPA risk assessment where one exists. Together they help you judge what actually matters for your health.
Words to know
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Common questions
What is the Report on Carcinogens?
It is a science-based public health document, required by Congress, that lists substances, mixtures, and exposures that may pose a cancer hazard to people in the United States. The National Toxicology Program prepares it.
What are its two categories?
'Known to be a human carcinogen' (sufficient evidence from human studies) and 'reasonably anticipated to be a human carcinogen' (limited human evidence, or sufficient animal evidence, or mechanistic grounds).
How is it different from IARC?
The RoC is a U.S. federal list with two categories; IARC is the WHO's international program with four groups. Both identify hazard rather than calculating personal risk, and their conclusions are usually similar but not identical.
What's new in the latest edition?
The 15th edition (2021) added chronic H. pylori infection as a new 'known' carcinogen, plus antimony trioxide and six haloacetic acids (water-disinfection byproducts) as 'reasonably anticipated.'
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Last updated: 2026-08-18Next planned review: 2028-07-05
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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