New Carcinogens Added to Toxicology List

Jan Dyer

March 08, 2022

From environmental tobacco smoke to ultraviolet (UV) radiation, diesel exhaust particulates, lead, and now, chronic infection with Helicobacter pylori (H pylori) —the Report on Carcinogens has regularly updated the list of substances known or "reasonably anticipated" to cause cancer.

The 15th report, which is prepared by the National Toxicology Program (NTP) for the Department of Health and Human Services, has 8 new entries, bringing the number of human carcinogens (eg, metals, pesticides, and drugs) on the list to 256. (The first report, released in 1980, listed 26.) In addition to H pylori infection, this edition adds the flame-retardant chemical antimony trioxide, and 6 haloacetic acids found as water disinfection byproducts.

In 1971, then President Nixon declared "war on cancer" (the second leading cause of death in the US) and signed the National Cancer Act. In 1978, Congress ordered the Report on Carcinogens, to educate the public and health professionals on potential environmental carcinogenic hazards.

Perhaps disheartening to know that even with 256 entries, the list probably understates the number of carcinogens humans and other creatures are exposed to. But things can change with time. Each list goes through a rigorous round of reviews. Sometimes substances are "delisted" after, for instance, litigation or new research. Saccharin, for example, was removed from the ninth edition. It was listed as "reasonably anticipated" in 1981, based on "sufficient evidence of carcinogenicity in experimental animals." It was removed, however, after extensive review of decades of saccharin use determined that the data were not sufficient to meet current criteria. Further research had revealed, also, that the observed bladder tumors in rats arose from a mechanism not relevant to humans.

Other entries, such as the controversial listing of the cancer drug tamoxifen, walk a fine line between risk and benefit. Tamoxifen, first listed in the ninth report (and still in the 15th report), was included because studies revealed that it could increase the risk of uterine cancer in women. But there also was conclusive evidence that it may prevent or delay breast cancer in women who are at high risk.

Ultimately, the report's authors make it clear that it is for informative value and guidance, not necessarily a dictate. As one report put it: "Personal decisions concerning voluntary exposures to carcinogenic agents need to be based on additional information that is beyond the scope" of the report.

"As the identification of carcinogens is a key step in cancer prevention," said Rick Woychik, PhD, director of the National Institute of Environmental Health Sciences and NTP, "publication of the report represents an important government activity towards improving public health."

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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