The U.S. Department of Health and Human Services (HHS) has added seven new substances, including viruses that have been linked to lymphoma in humans, to the list of human carcinogens, which now totals 248 substances that are known or are reasonably anticipated to cause cancer in humans.
This report identifies a number of environmental factors including chemicals; physical agents like X-rays and ultraviolet radiation; infectious agents such as viruses; and mixtures of chemicals. Each substance is either known to be a human carcinogen or is reasonably anticipated to be one.
The NTP has now included the chemical trichloroethylene (TCE), the cobalt element and cobalt-containing compounds, and five viruses that have been linked to cancer in humans.
Among the five viruses are four known to cause lymphoma.
“Given that approximately 12 percent of human cancers worldwide may be attributed to viruses, and there are no vaccines currently available for these five viruses, prevention strategies to reduce the infections that can lead to cancer are even more critical,” Linda Birnbaum, PhD, director of the National Institute of Environmental Health Sciences (NIEHS) and National Toxicology Program (NTP), said in a news release.
“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. There are also things people can do to reduce their exposure to cobalt and TCE,” she said.
The five virus included in the report are:
- Human immunodeficiency virus type 1 (HIV-1): It is spread through sexual activity, infected drug needles, or breastfeeding, and attacks the immune system, causing AIDS and leaving HIV-infected people more susceptible a variety of cancer types, including Hodgkin’s and non-Hodgkin’s lymphomas.
- Human T-cell lymphotropic virus type 1 (HTLV-1): Also spread through breastfeeding, infected needles, or sexual activity, this virus has been associated with the development of adult T-cell leukemia-lymphoma.
- Epstein-Barr virus (EVB): Primarily transmitted through saliva, this herpesvirus infects more than 90 percent of adults worldwide, most of whom remain healthy. It is commonly known for causing mononucleosis, but epidemiological studies have shown that it increases the risk of Burkitt lymphoma, Hodgkin’s lymphoma, immune-suppression-related non-Hodgkin’s lymphoma, and nasal type extranodal NK/T-cell lymphoma, as well as two types of epithelial cancer.
- Kaposi sarcoma-associated herpesvirus (KSHV): Another herpesvirus transmitted through saliva or sexual contact, KSHV has been linked to two rare types of lymphoma and to Kaposi sarcoma.
- Merkel cell polyomavirus (MCV): Commonly found in the skin, this virus rarely causes symptoms or leads to the development of cancer, but studies have suggested a link between infection with MCV and Merkel cell carcinoma.
In addition to these five virus, the NTP also re-evaluated TCE, which was listed as a reasonably anticipated human carcinogen since 2000, and has now been included as known to be a human carcinogen. The decision was supported by human studies showing a causal association between TCE exposure and increased risk of kidney cancer.
TCE is an industrial solvent used to make hydrofluorocarbon chemicals, which are gases used for refrigeration and air conditioning. It is also used as a metal degreasing agent to maintain military equipment, and is found in the groundwater at military sites.
Cobalt and cobalt-containing compounds that release cobalt ions in vivo were also included in the list as reasonably anticipated to be a human carcinogen, due to findings in animal models. Cobalt is commonly used in military and industrial equipment, as well as rechargeable batteries, and people are mainly exposed in the workplace or from failed surgical implants.