The Report on Carcinogens, 14th Edition, recently released by the U.S. Department of Health and Human Services (HHS), includes seven newly reviewed substances, bringing the cumulative total to 248 listings.
Five viruses linked to cancer in humans have been added to the list, along with the chemical trichloroethylene (TCE), and the metallic element cobalt and cobalt compounds that release cobalt ions in vivo. The five viruses include human immunodeficiency virus type 1 (HIV-1), human T-cell lymphotropic virus type 1 (HTLV-1), Epstein–Barr virus (EBV), Kaposi sarcoma-associated herpesvirus (KSHV), and Merkel cell polyomavirus (MCP). Collectively, these viruses have been linked to more than 20 types of cancers, according to the HHS report.
HIV-1 is spread through unprotected sexual activity, through infected drug needles, during pregnancy from mother to child, and through infected breast milk. The virus attacks the body’s immune system and causes acquired immune deficiency syndrome (AIDS). A weakened immune system is thought to increase a person’s risk of developing several cancers caused by other viruses, including non-Hodgkin’s and Hodgkin’s lymphomas; anogenital cancers, including penile, vaginal/vulvar, cervix, and anal; Kaposi’s sarcoma; oral-related cancers; and liver cancer. A weakened immune system also increases the risk of other types of cancers, including nonmelanoma skin cancer, eye cancer, and possibly lung cancer.
HTLV-1 is a virus that people are exposed to through contact with contaminated cells or biological tissues, such as breastfeeding, the sharing of needles or syringes with infected individuals, or unprotected sexual activity. It is not transmitted by casual contact. Human epidemiologic studies and molecular studies have shown that HTLV-1 causes adult T-cell leukemia–lymphoma, a rare cancer that infects the body’s own T cells, specifically the lymphocytes known as CD4 T cells, which help fight off infection.
EBV is a herpesvirus that is transmitted primarily through saliva. It is a common virus, infecting more than 90% of adults worldwide. Most people infected with EBV remain healthy and asymptomatic. In some cases, however, EBV can cause infectious mononucleosis. Human epidemiologic studies, clinical studies, and molecular studies have shown that EBV can lead to four types of lymphoma (Burkitt’s, Hodgkin’s, immune suppression-related non-Hodgkin’s, and nasal-type extranodal NK/T-cell) and two types of epithelial cancer (nasopharyngeal cancer and some types of stomach cancer).
KSHV is a herpesvirus transmitted from person to person 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 and show no signs or symptoms. There is sufficient human evidence linking KSHV to several cancers, including Kaposi’s sarcoma, and two rare lymphomas—primary effusion lymphoma and a specific plasmablastic variant of multicentric Castleman disease.
MCP is a common virus that lives on the skin, although it rarely produces symptoms or leads to cancer. Healthy people continuously shed MCP from the skin surface. Close personal contact with the saliva or skin of an infected individual may be how people are exposed to the virus. Human epidemiologic studies in different geographic locations, as well as clinical and molecular studies, have shown that MCP causes Merkel cell carcinoma.
Source: HHS; November 3, 2016.