Alan Frischer, MD, MPH
Viruses and Cancer
Updated: Dec 31, 2022
What causes cancer? In many cases, we have no idea. However, viruses, which most people think of as causing a nasty cold, have been identified as being responsible for certain cancers. That means that it is actually possible to prevent some of them!
Viruses are tiny organisms that are made up of a small number of genes in the form of DNA and RNA. In order to reproduce, a virus must enter a living cell. Some do this by inserting their own DNA or RNA into the host cell, thereby altering the host cell’s genetic makeup, and stimulating the development of cancer.
Our growing knowledge of this cancer-promoting role of viruses has led to the development of vaccines against them. However, these vaccines can only protect against infections if they are given prior to exposure.
Perhaps the most well-known cancer-causing virus is Human Papillomavirus (HPV). This is a group of more than 150 related viruses, about a dozen of which are known to cause cancer. So, although infections from HPV are extremely common, cancer from HPV is not.
They are spread through skin-to-skin contact. Most sexually active people are infected with one or more of these HPV types at some point in their lives. Some cause papillomas (warts). Some types of HPV only grow on skin, while others grow in the mucous membranes. There are no effective medications or treatments for HPV, other than removing or destroying the cells. Usually, the body’s immune system controls the HPV infection and gets rid of it over time.
A few strains of HPV are the main cause of cervical cancer, the second most common cancer among women. Cervical cancer rates have fallen, thanks to Pap smears and the HPV vaccine. Vaccination can help prevent more than 90% of HPV cancers. It works best when given early, before any exposure occurs, to boys and girls between ages 9 and 12 (but can be given later).
The Epstein-Barr virus (EBV) is a type of herpes virus, and is best known for causing infectious mononucleosis, also known as “mono” (the kissing disease). It can be spread by kissing, of course, as well as by coughing, sneezing, or sharing drinks or food. EBV infects more than 90% of the human population, increasing the risk of some cancers and some fast-growing lymphomas.
As with other herpes virus infections, EBV infection is life-long, although most symptoms are gone after the first few weeks. There are no medicines or treatments to get rid of EBV, and no vaccines to prevent it.
Certain types of chronic viral hepatitis can increase the odds of liver cancer. In the United States, some 65% of all liver cancer cases are linked to hepatitis B (HBV) or hepatitis C (HCV) infections. HCV infections may also be linked to non-Hodgkin lymphoma.
Both hepatitis B and C can now be treated with drugs, and in many cases cured. There is a vaccine to prevent HBV infection, but none yet for HCV. To see who is eligible for a hepatitis B vaccine, visit the CDC website.
Human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS). It does not cause cancers directly, but an active infection increases the risk. HIV is spread through semen, vaginal fluids, needles, during birth, breastfeeding, transfusions, organ transplants, and needle or instrument sticks. It is not spread through water, food, insects, or casual contact.
HIV infects and destroys white blood cells (helper T-cells), which weakens the immune system. It has been linked to a higher risk of developing Kaposi sarcoma and cervical cancer, certain kinds of non-Hodgkin lymphoma, anal cancer, lung cancer, cancer of the mouth and throat, some skin cancers, and liver cancer.
There is no vaccine to prevent HIV, but there are ways to lower the risk. Avoid unprotected sex or sharing needles. Those at high risk can use HIV prevention medications. And, while there is no cure, HIV can now be controlled with treatment.
The human herpes virus-8 (HHV-8) is also known as Kaposi sarcoma-associated herpesvirus. It has been found in nearly all tumors in patients with Kaposi sarcoma, a slow growing cancer that often appears as reddish-purple or blue-brown tumors. The HHV-8 virus is transmitted through sex and appears to be spread in other ways as well, including blood and saliva. It also appears in patients already weakened by an HIV infection; in fact, almost all individuals infected with HIV are also infected with HHV-8.
Two other extremely rare viruses that are associated with cancers are the human T-lymphotrophic virus-1 (HTLV-1) and Merkel cell polyomavirus (MCV).
So often, we do not understand how and why cancers appear. This makes it even more critical that we take advantage of all possible preventive measures. I urge you to discuss any of these vaccines and/or lifestyle changes with your doctor.