The National Institutes of Health (NIH) recently added seven newly reviewed substances, including five oncoviruses, to its 14th Report on Carcinogens (ROC). The ROC is a congressionally mandated scientific and public health document that identifies and discusses infectious agents, substances, mixtures, or exposure to certain substances that may pose a cancer hazard to humans. Its goal is to reduce exposure to cancer-causing compounds and viruses and to increase prevention. 

The five oncoviruses—HIV-1, HTLV-1, Epstein-Barr virus, Kaposi sarcoma-associated herpesvirus, and Merkel cell polyomavirus—have been linked to at least 20 cancers and are responsible for about 12% of cancers worldwide. They join hepatitis B, hepatitis C, and human papillomavirus on the list. 

All are considered “known human carcinogens.” This category is primarily used when there is sufficient evidence from human studies showing a cause-and-effect relationship between exposure and human cancer. Occasionally, substances are listed in this category based on human studies showing that the substance causes biological effects that lead to cancer. 

The agency also reclassified the heavy metal trichloroethylene (TCE), an industrial solvent used primarily to make hydrofluorocarbon chemicals. Trichloroethylene exposure occurs through the air, water, and soil where it is produced or used. It had been on the ROC since 1999 as a “reasonably anticipated” human carcinogen, meaning there was limited evidence of cancer in humans or sufficient evidence in experimental animals showing a cause-and-effect relationship between exposure to the substance and cancer. New studies demonstrating carcinogenicity in humans led to its upgraded status as a known human carcinogen. 

The committee also added cobalt, a naturally occurring element used to make metal alloys and other metal compounds. The highest exposure occurs in the workplace and from failed surgical implants. The report notes that it is “reasonably anticipated to be a human carcinogen.” 

Listing substances in the ROC can lead to reduced exposure to carcinogens. The NIH committee highlighted the Massachusetts Toxic Use Reduction Act, in which companies had to report their use of these chemicals to the state. Between 1991 and 2014, the use of carcinogens or suspected carcinogens identified in the ROC and by other authoritative sources declined by 32%, with reported releases down 93%. 

 “The listings in this report, particularly the viruses, bring attention to the important role that prevention can play in reducing the world’s cancer burden,” said Linda Birnbaum, PhD, the director of the National Institute of Environmental Health Sciences and National Toxicology Program, in a statement.