The National Toxicology Program has added seven new substances to its 14th Report on Carcinogens, bringing the total number in this congressionally mandated report to 248. The latest additions are the chemical trichloroethylene; cobalt metal and compounds that release cobalt ions in vivo; and five viruses, including HIV-1.

The National Toxicology Program (NTP), headquartered at the National Institute of Environmental Health Sciences (NIEHS) in Bethesda, MD, has added seven new substances to its 14th Report on Carcinogens: trichloroethylene (TCE), a chemical; cobalt metal and compounds that release cobalt ions in vivo; and five viruses (http://ntp.niehs.nih.gov/go/roc14).

In all, this congressionally mandated report now contains 248 substances, each classified as “known” or “reasonably anticipated” to be a human carcinogen. The former category requires sufficient evidence from human studies showing a cause-and-effect relationship between exposure to the substance in question and cancer. Evidence for the latter category is primarily from animal studies or otherwise limited.

TCE, an industrial solvent, has been listed as a reasonably anticipated carcinogen since 2000. It is now reclassified as a known carcinogen, NTP having evaluated multiple human studies that showed a causal association between TCE exposure and an increased risk of kidney cancer.

The release of cobalt ions into the body is thought to be a key trigger of cell death, DNA damage, and, subsequently, cancer. In studies of rats and mice, animals exposed to cobalt metal or cobalt compounds developed tumors at different sites, including the pancreas and adrenal glands. However, given that the data on human cobalt exposure are insufficient, NTP has categorized this element, for now, as a reasonably anticipated carcinogen.

Collectively, the five viruses listed asknown carcinogens—HIV-1, human T-cell lymphotropic virus type 1 (HTLV-1), Epstein-Barr virus, Kaposi sarcoma-associated herpesvirus (KSHV), and Merkel cell polyomavirus—have been linked to more than 20 different cancers. For instance, HTLV-1 causes adult T-cell leukemia/lymphoma, a rare but often aggressive cancer of the immune system's CD4+ T cells. Besides giving rise to Kaposi sarcoma, a blood-vessel cancer, KSHV has been linked to two rare lymphomas: primary effusion lymphoma and a specific plasmablastic variant of Castleman disease.

graphic

This photomicrograph shows, with the use of fluorescent antibody staining, leukemia cells that contain the Epstein-Barr virus.

“There are no vaccines currently available for these five viruses,” Linda Birnbaum, PhD, director of the NIEHS and NTP, noted in a press statement, so “prevention strategies to reduce the infections that can lead to cancer are even more critical.” –Alissa Poh

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©2017 American Association for Cancer Research.
2017
American Association for Cancer Research.