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Environmental Factor

Environmental Factor

Your Online Source for NIEHS News

December 2016

Seven substances added to 14th Report on Carcinogens

The report, released Nov. 3, added trichloroethylene, cobalt and certain cobalt compounds, and five viruses linked to cancer in humans.

The U.S. Department of Health and Human Services released the 14th Report on Carcinogens (RoC) Nov. 3. The congressionally-mandated report, which is prepared by the National Toxicology Program (NTP), included seven newly reviewed substances, bringing the total to 248 listings.

The report lists a variety of environmental factors, collectively called substances, that are grouped into two categories — known to be a human carcinogen and reasonably anticipated to be a human carcinogen. The listings can include chemicals; mixtures of chemicals; infectious agents, such as viruses; and physical agents, such as X-rays and ultraviolet radiation.

Five viruses, a chemical, and a metallic element

The chemical trichloroethylene (TCE), and the metallic element cobalt and cobalt compounds that release cobalt ions in vivo, are being added to the list, as are five viruses linked to cancer in humans.

  • Human immunodeficiency virus type 1.
  • Human T-cell lymphotropic virus type 1.
  • Epstein-Barr virus.
  • Kaposi sarcoma-associated herpesvirus.
  • Merkel cell polyomavirus.

“We’ve worked with our technical advisors and other agency experts to develop materials that are not only strong science documents, but can also be used to educate the public on these new listings,” said Ruth Lunn, Dr.Ph.H., director of the NTP Office of the Report on Carcinogens. In addition to technical reports, NTP released separate fact sheets on the overall report(https://www.niehs.nih.gov/health/materials/14th_edition_of_the_report_on_carcinogens_508.pdf), the viruses, TCE, and the cobalt listing.

“The fact sheets provide information on the substance, typical exposures, scientific findings on health effects, as well as advice on reducing exposures, which is our ultimate goal,” Lunn explained.

Many factors play a role in cancer

A listing in the report indicates a cancer hazard, but does not by itself mean that a substance will cause cancer. Many factors play a role, including an individual’s susceptibility to a substance and the extent of exposure.

In the case of viruses, a weakened immune system may also be a contributing factor. People should talk to their health care providers about decreasing their cancer risk from viruses.

“Approximately 12 percent of human cancers worldwide may be attributed to viruses, and there are no vaccines currently available for these five viruses,” said NIEHS and NTP Director Linda Birnbaum, Ph.D.

“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,” she added. “There are also things people can do to reduce their exposure to cobalt and TCE.”

Cancer-causing viruses

All five viruses were added to the category of known to be a human carcinogen. Together, these viruses have been linked to more than 20 different types of cancer.

  • Human immunodeficiency virus type 1 (HIV-1) is a virus that is spread through unprotected sexual activity, infected drug needles, during pregnancy from mother to child, and through infected breast milk. The HIV virus attacks the body’s immune system and causes AIDS. The weakened immune system is thought to increase a person’s risk of getting several cancers caused by other viruses, including non-Hodgkin and Hodgkin lymphomas; anogenital cancers, including penile, vaginal/vulvar, cervix, and anal; Kaposi sarcoma; and possibly oral-related cancers and liver cancer. HIV-1 also increases the risk of other types of cancers, including non-melanoma skin cancer, eye cancer, and possibly lung cancer.
  • Human T-cell lymphotropic virus type 1 (HTLV-1) is a virus that people are exposed to through contact with contaminated cells or biological tissues, such as during breastfeeding, sharing of needles or syringes with infected individuals, or unprotected sexual activity. It is not transmitted by casual contact. Human epidemiological studies and molecular studies show that HTLV-1 causes adult T-cell leukemia-lymphoma, a rare cancer that infects the body’s own T cells, specifically the white blood cells known as CD4 T cells, which help fight off infection.
  • Epstein-Barr virus (EBV) is a herpesvirus, transmitted primarily through saliva. It is a common virus, infecting more than 90 percent of adults worldwide. Most people infected with EBV remain healthy and without symptoms. In some cases, EBV can cause infectious mononucleosis, also called mono. Human epidemiological studies, clinical studies, and molecular studies show that EBV can lead to four types of lymphoma — Burkitt, Hodgkin, immune-suppression−related non-Hodgkin, and nasal type extranodal NK/T-cell — and two types of epithelial cancer — nasopharyngeal cancer and certain types of stomach cancer.
  • Kaposi sarcoma-associated herpesvirus (KSHV) is a herpesvirus transmitted primarily through saliva. It can be transmitted through sexual contact, primarily among men who have sex with men. It can also be spread through blood, and transmitted from an infected mother to a child. Healthy individuals can be infected with the virus yet show no signs or symptoms. There is sufficient human evidence linking KSHV to several cancers, including Kaposi sarcoma, and two rare lymphomas — primary effusion lymphoma and a specific plasmablastic variant of multicentric Castleman disease.
  • Merkel cell polyomavirus (MCV) is a common virus that lives on the skin, though it rarely produces symptoms or leads to cancer. Healthy people continuously shed MCV from the skin surface. Close personal contact with saliva or skin of an infected individual may be how people are exposed to the virus. Human epidemiology studies in populations in different geographic locations, as well as clinical and molecular studies, show that MCV causes Merkel cell carcinoma.


TCE is an industrial solvent used primarily to make hydrofluorocarbon chemicals. The new RoC lists TCE as a known human carcinogen. In 2000, it was listed as a reasonably anticipated human carcinogen. However, numerous human studies showing a causal association between TCE exposure and an increased risk for kidney cancer led NTP to re-evaluate the solvent.

People can be exposed to TCE through a variety of routes. It can be released into the air, water, and soil at places where it is produced or used. TCE breaks down slowly and can move readily through soil to make its way into underground drinking water sources. Because of its widespread use as a metal degreasing agent to maintain equipment, it has been found in the groundwater at many military and Superfund sites.

Cobalt and certain cobalt compounds

Cobalt and cobalt compounds that release cobalt ions in vivo were listed as reasonably anticipated to be a human carcinogen. The listing for cobalt includes different types of cobalt compounds that release ions into the body. It does not include vitamin B-12, because cobalt in this essential nutrient is bound to protein and does not release cobalt ions.

Cobalt is a naturally occurring element used to make metal alloys and other metal compounds, such as military and industrial equipment, and rechargeable batteries. The highest exposure occurs in the workplace and from failed surgical implants. This listing is based largely on studies in experimental animals and supporting mechanistic data, which formed the basis for grouping cobalt in a class with cobalt compounds that release cobalt ions in vivo.

(Robin Mackar is news director in the NIEHS Office of Communications and Public Liaison and a frequent contributor to the Environmental Factor.)


This image from the TCE fact sheet shows possible routes of exposure to TCE, including workplace, closed military and industrial sites, as well as movement through air, soil, and groundwater.

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