Viruses can cause cancer, but there is tremendous ongoing research on improving prevention and treatment outcomes for these cancers.

Approximately 15% of human cancers globally are known to have a viral etiology, and this percentage likely will grow as researchers identify new human viruses and investigate viral causes for more cancers. It is an increasingly important global public health concern.

Several viruses, known as oncogenic viruses, are associated with cancer. At least 7 viruses have been associated with cancer risk, including Epstein-Barr virus (EBV), hepatitis B virus (HBV), human papillomavirus (HPV),  human T-cell lymphotropic virus (HTLV), hepatitis C virus (HCV), Kaposi’s sarcoma (HIV) , herpes virus, and Merkel cell polyomavirus. These viruses can increase cancer risk through different mechanisms, including:

• Disrupting the signaling pathways of cellular genes, either by mutation or by tampering with how genes are expressed, affects cell growth.
• Suppressing or weakening the immune system
• Causing chronic, long-term inflammation

It’s important to remember that most viral infections do not lead to cancer. There are several factors that influence whether infection with an oncogenic virus will progress to cancer, usually many years after the initial exposure. These can include things like the health of your immune system, chronic health conditions, exposure to other risk factors, genetics, and the environment. Here is a brief explanation of how some of the more common viruses increase your cancer risk:

Epstein-Barr Virus (EBV):

EBV is a type of herpes virus also known to cause infectious mononucleosis, or mono, as it is commonly known. This virus is most often spread through saliva via coughing, sneezing, kissing, or sharing personal items such as toothbrushes or drinking or eating utensils. It also spreads via sexual contact and blood transfusions. Most people in the United States are infected with EBV by the end of their teen years. Once you have an EBV infection, the virus lives inside you (in your white blood cells) for the rest of your life, even though most people have no symptoms after the first few weeks. There are no vaccines, medicines, or other treatments to get rid of EBV, but it helps that EBV infection doesn’t cause serious problems in most people.

EBV infection does increase the risk of Burkitt lymphoma, some types of Hodgkin’s and non-Hodgkin’s lymphoma, post-transplant lymphoproliferative disease, leiomyosarcomas, head and neck cancers, and stomach cancer. EBV-related cancers are more common in Africa and parts of Southeast Asia. Remember that, overall, very few people who have been infected with EBV will ever develop these cancers.

Hepatitis B and Hepatitis C Virus (HBV & HCV):

HBV and HCV are spread between people through sharing needles (such as during injection drug use), unprotected sex, or childbirth. They can also be passed on through blood transfusions, but this is quite rare in the United States because donated blood is tested for these viruses. Infection with HBV usually causes a flu-like illness and jaundice (yellowing of the eyes and skin). Most adults recover completely from HBV infection within a few months. However, some people end up with chronic HBV infections and have a higher risk for liver cancer. HCV is less likely to cause symptoms than HBV, but it is more likely to cause chronic infection, which can lead to liver damage or, subsequently, cancer. An estimated 3.2 million people in the United States have chronic HCV infection, and most of these people don’t even know they have it. The Centers for Disease Control and Prevention (CDC) recommend that all people born between 1945 and 1965 (as well as some other people at high risk) get blood tests to check for HCV. In the United States, less than half of liver cancers are linked to HBV or HCV infection.

Some research also suggests that long-term HCV infection might be linked with some other cancers, such as non-Hodgkin's lymphoma. Both hepatitis B and C infections can be treated with drugs. Treating chronic hepatitis C infection with a combination of drugs for at least a few months can get rid of HCV in many people. A number of drugs can also be used to help treat chronic hepatitis B. There is a vaccine to prevent HBV infection, but none for HCV. In the United States, the HBV vaccine is recommended for all children. It’s also recommended for adults who are at risk of exposure.

Human Papilloma Virus (HPV):

There are more than 100 types of HPV, of which at least 14 are cancer-causing (also known as high risk type). Two HPV types (16 and 18) cause 70% of cervical cancers and pre-cancerous cervical lesions.

All types of HPV are spread by physical contact. More than 40 types of HPV can be passed on through sexual contact. Most sexually active people are infected with one or more of these HPV types at some point in their lives. At least a dozen of these types are known to cause cancer.

While HPV infections are very common, cancer caused by HPV is not. Most people infected with HPV will not develop cancer related to the infection. However, some people with long-lasting infections with high-risk types of HPV are at risk of developing cancer. HPV16 and HPV18 are high-risk strains that are responsible for most cancers. HPV vaccination can prevent over 90% of cancers caused by HPV, as well as anal, vaginal, cervical, and vulvar cancers, but it works best when given at age 11–12 years, before contact with the HPV virus.

Human Immunodeficiency Virus (HIV):

HIV is the virus that causes acquired immunodeficiency syndrome (AIDS) but does not appear to cause cancer directly. HIV infection, however, increases a person’s risk of getting several types of cancer, especially some linked to other viruses. HIV can be spread via:

• Unprotected sex (oral, vaginal, or anal) with an HIV-infected person
• Injections with needles or injection equipment previously used by an HIV-infected person
• Prenatal (before birth) and perinatal (during birth) exposure of infants from mothers with HIV
• Breastfeeding by mothers with HIV
• Penetrating injuries or accidents (usually needle sticks) in health care workers while caring for HIV-infected patients or handling their blood

HIV is not spread through saliva, treats, sweat, or casual contact. The risk of getting HIV via blood transfusion or organ transplant is less than 1 in a million because of the required screening of blood and blood products as well as donor screening. HIV infects and destroys white blood cells known as helper T-cells, which weaken the body’s immune system. A weak immune system might let new cancer cells survive long enough to grow into a full-fledged cancer. HIV infection has been linked to a higher risk of developing Kaposi sarcoma and cervical cancer. It’s also linked to certain kinds of non-Hodgkin lymphoma, especially central nervous system lymphoma. Some other, less common types of cancer may also be more likely to develop in people with HIV. The CDC recommends that everyone between the ages of 13 and 64 be tested for HIV at least once as part of their routine health care.

There is no vaccine to prevent HIV. But there are ways to lower your risk of getting it, such as not having unprotected sex or sharing needles with someone who has HIV, as well as being on anti-HIV medications if you have an HIV infection.

Keep in mind that having an infection by an oncogenic virus doesn’t mean you’ll develop cancer. 

It simply means you may have a higher risk than someone who’s never had the infection. It is important to understand that risk factors present an opportunity to decrease your chances of getting cancer and develop healthy behaviors as part of living up to your potential.