How Some Viruses Cause Cancer

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Most of the time, the effects of a virus are short-lived and relatively mild, like a common cold. However, sometimes these microorganisms can cause more substantial harm, and the long term effects of certain viruses may include complications such as cancer. 

Around 10% of cancer cases worldwide are thought to be caused by viruses, and the majority of these affect people in developing countries. Many virus-associated cancers can take years to become symptomatic, which makes it difficult to know this percentage with certainty.

A woman receiving a vaccine
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How a Virus Causes Cancer

All viruses are composed of genetic material (which may be DNA or RNA) enclosed in a protein coat. Viruses have the ability to invade a "host," such as a human or animal.

Sometimes this invasion causes cancer through the oncogenesis—a multistep process in which healthy cells undergo certain genetic mutations (errors in the genetic material) that lead to cancer.

There are several ways that a virus can cause cancer:

  • Directly damage DNA in host cells, resulting in cancer
  • Altering the immune system so that it is less able to fight off cancer cells (which could have initially developed due to something other than the virus)
  • Chronic inflammation
  • Disrupting the body's normal regulation of cell division

Whenever cells divide, there is a risk that a genetic mutation will take place. Some viruses lead to inflammation or tissue damage that triggers increased cell division—which leads to a greater chance that mutations will take place, eventually leading to cancer.

Viruses Known to Cause Cancer

A number of different viruses have been associated with cancer. Both DNA or RNA viruses can cause cancer. Typically, a virus causes a specific type or a few types of cancer due to the way it interacts with the body.

HTLV-1 is a retrovirus (similar to HIV) that causes adult human T-cell leukemia/lymphoma. HHV-8 (also known as Kaposi sarcoma herpes virus, KSHV) can cause Kaposi's sarcoma. Merkel cell polyomavirus (McPyV) can cause Merkel cell carcinoma, a form of skin cancer. The virus is very common in the population as a whole, but cancer associated with the McPyV virus is uncommon.

If you have been diagnosed with a virus that is associated with cancer, you could be at increased risk of developing the associated type of cancer. If you have a known risk, it is important that you keep up with recommended screenings and preventative strategies to avoid the potentially serious consequences of cancer.

Human Papillomavirus (HPV) and Cancer

The human papillomavirus (HPV) is a sexually transmitted virus affecting nearly 80 million Americans. It is the most common type of sexually transmitted infection.

There are currently over one hundred known strains of HPV, but only a small portion of these are thought to cause cancer. The strains of HPV most commonly associated with cancer include HPV 16 and HPV 18.

Vaccination for HPV—a shot that protects against HPV 16 and HPV 18—is available for children between the ages of 11 and 12, and can be given starting at age 9 and as old as age 26.

The detection of the DNA of HPV virus is found in:

  • Cervical cancer: 90%
  • Vulvar cancer: 69%
  • Anal cancer: 91%
  • Vaginal cancer: 75%
  • Penile cancer: 63%
  • Head and Neck cancer: 30% of mouth cancers and 20% of throat cancers

In some other cancers, the data is less certain. For example, HPV is linked to lung cancer, but it's not known if HPV contributes to the development of lung cancer.

Hepatitis B and Cancer

Viral hepatitis B infections are extremely contagious are spread through the transmission of blood, semen, and other bodily fluids from one person to another. Common means of exposure include unprotected sex, mother to infant transmission during childbirth, and the sharing of intravenous needles (most often by drug use, and can also occur during tattooing).

Most people recover from an acute hepatitis B infection, but some people go on to develop a chronic hepatitis B infection. Chronic infections are more common among those who contract the disease in early childhood and those who do not have any symptoms.

Infection with Hepatitis B virus (HBV) increases the risk of developing liver cancer. Liver cancer occurs more often among those with chronic hepatitis B.

Most children born since the 1980s have been immunized against hepatitis B, and adults who have not been immunized may discuss this option with their doctors.

Hepatitis C and Cancer

Hepatitis C infection also increases the risk of developing liver cancer. The virus is spread through infected blood, such as with transfusions and IV drug abuse, but many people do not have obvious risk factors for the infection.

The initial infection may produce symptoms, but you can have a silent infection without any noticeable effects. As the immune system attacks the virus over time, liver fibrosis (scarring) develops, eventually leading to cirrhosis (cell death). This chronic inflammation can lead to liver cancer.

It is now recommended that adults born between 1945 and 1965 be tested for the disease, as well as others who may be at risk.

Epstein-Barr Virus (EBV) and Cancer

The Epstein-Barr virus most commonly causes mononucleosis but is also known to cause nasopharyngeal carcinoma and gastric carcinoma. Additionally, this virus is linked with the development of several different types of lymphoma, including:

  • Posttransplant lymphoma: Between 1 and 20% of people develop lymphoma after an organ transplant, and almost all of these are related to Epstein-Barr virus infections.
  • HIV-associated lymphoma: Over 90% of HIV associated lymphoma is related to EBV.
  • Burkitt's lymphoma: In Africa, Burkitt's lymphoma is responsible for over half of all childhood cancers, and nearly all of these are linked to the Epstein-Barr virus.
  • Hodgkin's lymphoma: It's thought that the Epstein-Barr virus plays a role in 30 to 50% of cases of Hodgkin disease in the U.S.

Human Immunodeficiency Virus (HIV) and Cancer

HIV and cancer are linked in several ways. Non-Hodgkin lymphoma, Hodgkin lymphoma, primary CNS lymphoma, leukemia, and myeloma are all linked with HIV infection. In addition to lymphomas, HIV increases the risk of Kaposi's sarcoma, cervical cancer, lung cancer, anal cancer, and liver cancer.

The immunosuppression caused by the HIV virus can predispose people with the disease to cancer because immune cells do not effectively fight cancer cells when a person is infected with HIV. Because HIV weakens the immune system, the cancer cells caused by Epstein Barr virus or by any other mutation can proliferate and survive—causing a person to develop severe illness from cancer.

HIV infection also causes certain immune cells (B cells) to proliferate, increasing the risk of overproduction and mutation, which can lead to B cell cancers.


Many of the viruses that can lead to cancer are passed from person to person. Some bacteria and parasites are linked with the development of cancer as well. Prevention is a key component of avoiding cancer as a complication of any infection.

Practicing safe sex and not sharing needles are two ways to lower risk. The importance of being healthy in general—eating right and exercising—is reinforced in seeing how suppressed immune function can raise the risk of some of the viral-induced cancers.

Prevention of cancer caused by viruses is a developing area of research—especially the emergence of prevention through vaccines.

Additionally, researchers are working on strategies that use viruses to fight cancer.

A Word From Verywell

It's important to note that most viruses do not cause cancer. Even when viruses produce cancer-associated genetic mutations, most of the damaged cells are removed by a healthy immune system. 

When a viral infection or any other type of infection leads to the production of cancer cells that are able to escape the immune system, there are often other factors at work, such as a weak immune system.

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