6 Viruses That Can Lead to Cancer

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A Minority of Infections Become Cancerous

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No one type of virus causes cancer. The six different viruses that can cause cancer come from different virus families, have varied genomes, and have different life cycles.  

Overall, infection with any of these viruses is very common. Fortunately, only a minority of people infected with these viruses ever go on to develop cancer. And if cancer were to develop, it would take years or even decades to take hold. Furthermore, viruses on their own are insufficient to cause cancer and must also accompany immunosuppression, somatic mutations, genetic predisposition, and exposure to carcinogens.

Here are six types of viruses that cause cancer (aka human tumor viruses):


  

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Hepatitis C

Hepatitis C
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Hepatitis C is an RNA virus. It causes both acute and chronic hepatitis. Chronic infection with hepatitis C causes cirrhosis or scarring of the liver. In 1 to 2 percent of those infected, this cirrhosis can eventually lead to hepatocellular (liver) cancer. Hepatitis C has also been linked to non-Hodgkin's lymphoma.

Although researchers have yet to develop a vaccine for hepatitis C, effective treatments for the disease exist, including Olysio, Sovaldi, and Harvoni.

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Hepatitis B

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Whereas hepatitis C is an RNA virus, hepatitis B is a DNA virus. Despite being a different class of virus, hepatitis B causes infection with a clinical course similar to hepatitis C: acute and chronic hepatitis, cirrhosis, and hepatocellular cancer. 

Hepatocellular cancer is an aggressive cancer that kills a year or two after infection. Treatment for hepatocellular cancer culminates in surgical resection of the liver or liver transplant.

Fortunately, we have a vaccine for hepatitis B.

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Human Papilloma Virus (HPV)

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HPV is a small DNA virus that causes genital warts. Recurrent infection with high-risk subtypes of HPV can result in cervical cancer. Moreover, persistent HPV infection has also been implicated in the development of other types of cancer, including head and neck tumors, skin cancers in immunosuppressed patients (think AIDS), and anogenital cancers.

Fortunately, thanks to the PAP smear, we have highly effective early screening for cervical cancer.

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Human T Lymphocyte Virus Type 1 (HTLV-1)

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HTLV-1 is an RNA retrovirus. Across the world, 5 to 25 million people are infected with this virus; however, only a minority (5 percent) develop symptoms. HTLV-1 has a tropism or attraction to CD4 cells, a leukemia clonal cell. Twenty to thirty years after infection with HTLV-1, adult T-cell leukemia can develop.   

Chemotherapy can initially be used to treat adult T-cell leukemia and results in short-term remission followed by quick recurrence of the disease. The (median) survival time after development of adult T-cell leukemia is 8 months.

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Epstein-Barr Virus

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EBV is a ubiquitous virus that we're all familiar with—it causes mononucleosis. Although 95 percent of people contain EBV on throat culture, most infections are subclinical, with a minority of people developing clinical disease.

EBV has been linked to a variety of cancers including B- and T-cell lymphomas, leiomyosarcomas, nasopharyngeal carcinomas, Hodgkin’s disease, and post-transplant lymphoproliferative disease.

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HHV-8 or Kaposi Sarcoma Herpesvirus

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In 1994, HHV-8, or Kaposi sarcoma herpesvirus, was implicated in the development of Kaposi's sarcoma, a cancer which causes skin and mouth lesions (sores) in those with AIDS. However, in those with stronger immune systems, HHV-8 is rarely malignant.

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Future Therapeutic Directions for Human Tumor Viruses

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Novel therapeutic approaches to cancer caused by human tumor viruses focus on viral gene products that are specific to tumor cells caused by the virus. By developing treatments that specifically target cells which have been infected by viruses, future treatment options can spare the body's healthy cells. Currently, treatments like chemotherapy and radiotherapy kill all cells, which explains their nasty and severe adverse effects.

Currently, the best way to prevent cancer secondary to human tumor viruses (however rare) is to prevent exposure to human tumor viruses themselves. Although some of these viruses are ubiquitous, we can prevent exposure to certain of these viruses like hepatitis B and C. There are also hepatitis B and HPV vaccinations available.

Sources:

Liao JB. Viruses and Human Cancer. Yale Journal of Biology and Medicine. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1994798/

Mazzaro C et al. Hepatitis C virus and non-Hodgkin's lymphoma 10 years later. Digestive Liver Disease. https://www.researchgate.net/publication/7948031_Hepatitis_C_virus_and_non-Hodgkin's_lymphoma_10_years_later

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