Today, it is estimated that viruses are responsible for almost 20 percent of cancer cases worldwide. Seven viruses have been connected to specific types of malignancies. They include:
- Human papillomaviruses (HPVs), a group of more than 150 related viruses that are spread by contact. At least a dozen of them are known to cause cancer, including cervical cancer and some types of head and neck cancer. Certain HPVs also have a role in penile, anal, vaginal, and vulvar cancers. While infection with one or more HPVs is very common, cancers arising from these infections are rare and are more likely to occur in people with long-lasting infections of certain high-risk types of HPV. Vaccination against the three main cancer-causing types of HPV can prevent more than 90% of HPV-related cancers and is available for children and young adults.
- Epstein-Barr virus (EBV), a type of herpes virus that causes mononucleosis. Infection with EBV increases a person’s risk of nasopharyngeal cancer, certain types of fast-growing lymphomas, and, possibly some cases of Hodgkin lymphoma and stomach cancer. There are no medicines to eliminate EBV from the body and no vaccines to prevent it, but EBV infection doesn’t cause serious problems in most people.
- Hepatitis B and Hepatitis C viruses (HBV and HBC), which cause hepatitis, an infection of the liver. They can be spread by sharing needles, unprotected sex, or blood transfusions (although this is rare in the U.S. as donated blood is tested for them). Long-term infection with either HBV or HBC can increase a person’s likelihood of developing liver cancer. There is a vaccine to prevent HBV infection but not for HCV. In the United States, the HBV vaccine is recommended for all children and for adults up to age 59.
- Human immunodeficiency virus (HIV), the virus responsible for AIDS, doesn’t cause cancer directly, but, by undermining the immune system, can make some cancers more likely. HIV can be spread through semen, vaginal fluids, blood, and breast milk from an HIV-infected person. HIV infection has been linked to a higher risk of Kaposi sarcoma, cervical cancer, and certain kinds of non-Hodgkin lymphoma. While there is no vaccine to prevent HIV infection, anti-HIV drugs can help people who are already infected.
- Human herpes virus 8 (HHV-8) has been found in nearly all tumors in patients with Kaposi sarcoma, a cancer that forms in cells lining blood and lymph vessels. The virus is transmitted through sex and, research suggests, through blood a saliva as well. Fewer than 10% of people in the United States are infected with the virus, which does not cause disease is most health individuals.
- Human T-lymphotrophic virus-1 (HTLV-1) has been linked to a form of lymphocytic leukemia and to a form of non-Hodgkin lymphoma called adult T-cell leukemia/lymphoma. Found mostly in Japan, the Caribbean, central Africa, and parts of South America, HTLV-1 is a retrovirus, whose genetic code is written in RNA rather than DNA.
- Merkel cell polyomavirus (MCV) has been found in tissue samples of a rare, aggressive type of skin cancer called Merkel cell carcinoma. Most people infected with MCV experience no symptoms, but a few go on to develop Merkel cell carcinoma.
How viruses cause cancer
While viruses can cause cancer in a variety of ways, the actual mechanisms fall into two broad categories. In the direct method, oncoviruses (cancer-causing viruses) infect normal cells and slip some of their genes into the cells’ DNA, causing the cells to produce a few abnormal proteins. If the cells acquire additional gene mutations, or if the individual has a weakened immune system, the cells can begin to behave cancerously.
In the other, indirect, method, viral infection can cause tissue to become inflamed as the immune system tries to quell the infection. Such inflammation, persisting for years or even decades, increases the chances that tissue will become cancerous.
Research into vaccines for virus-associated cancers is moving on several fronts. Dana-Farber’s Cancer Vaccine Center is pioneering new technologies and approaches that will help create more effective cancer vaccines in the future. Vaccines may not be right for everyone. It is important to discuss options — and potential side effects — with your physician.
About the Medical Reviewer
Dr. Wucherpfennig received his MD in 1986 and his PhD in 1987 from the University of Goettingen, Germany. He completed research fellowships at Brigham and Women's Hospital and the Department of Molecular and Cellular Biology, Harvard University. In 1995, he joined DFCI, where he is principally involved in basic laboratory research that focuses on T cell immunology and the role of T cells in cancer immunology.