The U.S. Report on Carcinogens (NTP), Explained

The U.S. counterpart to IARCExplain▾

Alongside the WHO's IARC Monographs, the United States has its own respected carcinogen list: the Report on Carcinogens (RoC), prepared by the National Toxicology Program (NTP), 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 that identifies substances, mixtures, and exposures that may pose a cancer hazard to people in the United States.

Two categoriesExplain▾

Where IARC uses four groups, the RoC uses just two categories:

• "Known to be a human carcinogen." There is sufficient evidence from studies in people showing 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, or strong mechanistic grounds to expect the agent can cause cancer.

The 15th edition (2021) contains 256 listings — 63 "known" and 193 "reasonably anticipated."

Hazard, not risk — againExplain▾

Just like IARC, the RoC performs hazard identification. A listing means the substance can pose a cancer hazard — not that any particular exposure will cause cancer in an individual. The NTP is careful to make this distinction. Whether a listed substance poses real-world risk depends on how much, how often, and how long a person is exposed.

What's new in the latest editionExplain▾

The 15th edition (2021) added eight new listings, which give a sense of how the process works:

• Chronic Helicobacter pylori infection — the only new "known" carcinogen, linked to stomach cancer.
• Antimony trioxide — "reasonably anticipated."
• Six haloacetic acids — byproducts of disinfecting drinking water — all "reasonably anticipated."

How it compares to IARCExplain▾

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. Because both identify hazard, the same hazard-versus-risk reasoning applies to both: a listing tells you the evidence is strong enough to flag a cancer hazard, not how much risk you personally face.

Why it's usefulExplain▾

The RoC is a trustworthy, government-vetted reference for whether a substance is recognized as a cancer hazard in the United States. Paired with real-world exposure information — and, where available, an EPA risk assessment — it helps you judge what actually matters for your health.