Viral infections and cancer Viruses are responsible for 12% of cancers worldwide. While some of these infections are common, they rarely result in cancer.   Worldwide, approximately 18% of cancers are caused by infections.1 Viruses are responsible for most of the cancers caused by infectious agents (12% of all cancers worldwide).1 There is an established link between human cancer and Human Papillomavirus (HPV), Hepatitis B Virus (HBV), Hepatitis C Virus (HCV), Human T-Cell Lymphotrophic/Leukemia Virus Type 1 (HTLV-1), Human Immunodeficiency Virus (HIV), Human Herpesvirus 8 (HHV-8), and Epstein-Barr Virus (EBV).2 These viruses can be responsible for a range of cancers. Prevention efforts around these agents include population screening, treatment, public education, and vaccines (in development or use). While some of these viral infections are common (e.g., with HPV and EBV), only rarely do they lead to cancer. Population screening (e.g., with the Pap test) is one way to prevent cancer that might result from a viral infection. Infectious agents can cause cancer through one or more of the following mechanisms: chronic inflammation from long-term infection, development of mutations/genetic changes, or immune suppression, e.g., from HIV infection.4 Most people’s bodies are able to control the infections; cancer may result when the host’s ability to do so is compromised.5 The cause of many cancers is unknown, or related to multiple factors, which makes prevention difficult. Because a cancer caused by a virus is related to a specific cause (i.e., the infection), there is hope that the cancer can be prevented or treated. A vaccine against HBV is available, and a preventive vaccine against some types of HPV (the virus that causes cervical cancer) recently became available to Ontario grade eight girls, in a school-based vaccination program.6 Over time, it is likely that more viruses will be linked with cancer, and efforts to prevent the cancers they cause will continue to improve. For more information, see: Cancer Care Ontario: Perspectives on Infectious Agents and Cancer. Toronto: Cancer Care Ontario 2010 at http://www.cancercare.on.ca/research/researchprograms/resnet/popstudies/ References Parkin DM. The global health burden of infection-associated cancers in the year 2002. Int J Cancer 2006; 118:3030–3044. Bouvard V, Baan R, Straif K, et al. on behalf of the WHO International Agency for Research on Cancer Monograph Working Group. Special report: Policy. A review of human carcinogens—part B: Biological agents. Lancet Oncol 2009; 10(4):321–2. International Agency for Research on Cancer. Agents classified by the IARC Monographs, Volumes 1-100. Lyon: World Health Organization 2010. Cancer Care Ontario. Perspectives on Infectious Agents and Cancer. Toronto: Cancer Care Ontario 2010. Mueller N. Overview: Viral Agents and Cancer. Environmental Health Perspectives 1995; 103(8):259–261. Backgrounder – Human Papillomavirus Immunization program [Internet]: Government of Ontario; c2007. Citation: Cancer Care Ontario. Cancer Fact: Viral infections and cancer. July 2010. Available at http://www.cancercare.on.ca/ocs/csurv/ont-cancer-facts/. Prepared by: Population Studies, Population Studies and Surveillance.