How can the virus cause cancer?

When you hear the word “viruses,” you might think of minor, temporary illnesses, such as a 24-hour cold or flu. But some viruses have also been linked to certain types of cancer. As the medical community has learned more about these links, they have developed vaccines that, by protecting against certain viral infections, help prevent cancer. A notable example is the human papillomavirus (HPV) vaccine, which was first developed just over a decade ago. “Knowledge of viruses and their potential relationships to cancer has increased over the past decade,” says Natalie Godbey, a gynecological oncologist at our hospital near Phoenix. “But there is always room for improvement.” Many of the viruses associated with cancer do not yet have vaccines designed to prevent them.

Viruses, infections and cancer

When viruses cause an infection, they spread their DNA, affecting the genetic makeup of healthy cells and potentially causing them to turn into cancer. HPV infection, for example, causes the virus’s DNA to combine with the host’s DNA, disrupting the normal function of cells. Other viruses, such as the human immunodeficiency virus (HIV) and hepatitis C virus (HCV), can increase a person’s risk of developing cancer by affecting the body’s immune system. In most cases, certain viruses only affect certain cells in the body, such as the common cold viruses that affect the lining of the nose and throat. This is why some viruses are only linked to certain types of cancer.

Although most people infected with HPV do not develop cancer, some strong strains of the virus cause the vast majority of cervical cancers, which is the second most common type of cancer in women worldwide. “HPV causes about 98 percent of cervical cancer cases, so it’s very concerning,” says Dr. Goodby. Patients infected with HPV should have appropriate testing at the time of diagnosis, such as colposcopy, and should be routinely followed up with screenings. A Pap test, or Pap smear, allows doctors to detect precancerous changes in cervical cells, helping to facilitate early intervention efforts designed to prevent the development of cervical cancer. After the introduction of the Pap test in the 1950s, the incidence of cervical cancer decreased significantly, says Dr. Goodby.

But HPV is not only linked to cervical cancer. It’s also been linked to vaginal, vulvar, anal, and head and neck cancers, making educational efforts even more important for prevention. “We’ve known the link between HPV and cervical cancer for years, but most people don’t know that this virus can also be a direct link to these other cancers,” says Dr. Goodby. Although men get HPV at about the same rate as women, no screening test is available to diagnose HPV in men.

Common viruses associated with cancer

Other common types of viruses associated with cancer include:

• The Epstein-Barr virus (EBV) , the type of herpes virus most commonly associated with causing infectious mononucleosis, or “mono.” EBV infection increases the risk of developing nasopharyngeal cancer, some types of fast-growing lymphoma, and some stomach cancers. Like HPV, EBV infection is common, but EBV-related cancer is not.
• Hepatitis B virus (HBV) and HCV , which cause viral hepatitis, a type of liver infection. Chronic liver infections caused by hepatitis B and HCV are rare, but when they do occur, they increase the risk of developing liver cancer. Less than half of liver cancers in the United States are associated with hepatitis B virus or HCV infection.
• HIV , which causes acquired immunodeficiency syndrome (AIDS). HIV increases the risk of several types of cancer, including Kaposi’s sarcoma, cervical cancer, non-Hodgkin’s lymphoma, anal cancer, and lung cancer.