Risk Factors for Anal Cancer

A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking or diet, can be changed. Others, like a person’s age or family history, can’t.

Several factors can affect your risk of anal cancer. But having a risk factor, or even several risk factors, does not mean that you will get cancer. Many people with risk factors never develop anal cancer, while others with this disease may have few or no known risk factors.

Human papillomavirus (HPV) infection

Most squamous cell anal cancers are linked to infection with the human papillomavirus (HPV), the same virus that causes cervical cancer, as well as many other kinds of cancer. In fact, women with a history of cervical cancer (or pre-cancer) have an increased risk of anal cancer.

HPV is a group of more than 150 related viruses. They are called papillomaviruses because some of them cause papillomas, which are more commonly known as warts. There are many subtypes of HPV, but the one most likely to cause anal cancer is HPV-16. Other subtypes of HPV can cause warts in the genital and anal areas, but not cancer. The 2 types of HPV that cause most cases of anal and genital warts are HPV-6 and HPV-11. While anal warts themselves are unlikely to develop into anal cancer, people who have had anal warts are more likely to get anal cancer. This is because people who are infected with HPV subtypes that cause anal and genital warts are also more likely to be infected HPV subtypes that cause anal cancer.

HPV is passed from one person to another during skin-to-skin contact with an infected area of the body. HPV can be spread during sexual activity – including vaginal, anal, and oral sex – but sex doesn’t have to occur for the infection to spread. All that's needed is for there to be skin-to-skin contact with an area of the body infected with HPV. The virus can be spread through genital-to-genital contact, or even hand-to-genital contact. An HPV infection can also spread from one part of the body to another. For example, an HPV infection might start in the genitals and then spread to the anus.

It can be very hard to avoid being exposed to HPV. It might be possible to prevent genital HPV infection by not allowing others to have contact with your anal or genital area, but even then there could be other ways to become infected that aren’t yet clear.

Infection with HPV is common, and in most cases the body can clear the infection on its own. But in some people the infection doesn’t go away and becomes chronic. Chronic infection, especially with high-risk HPV types, can cause certain cancers over time, including anal cancer.

For more information, see HPV and HPV Vaccines.

Having certain other cancers

Women who have had cancer of the cervix, vagina, or vulva are at increased risk of anal cancer. This is probably because these cancers are also caused by infection with HPV.

In men, it would seem likely that having had penile cancer, which is also linked to HPV infection, would increase the risk of anal cancer, but this link has not been shown in studies.

HIV infection

People infected with the human immunodeficiency virus (HIV), the virus that causes AIDS, are much more likely to get anal cancer than those not infected with this virus. For more information about HIV and AIDS, see HIV Infection, AIDS, and Cancer.

Sexual activity

Having multiple sex partners increases the risk of infection with HIV and HPV. It also increases the risk of anal cancer.

Receptive anal sex also increases the risk of anal cancer in both men and women. Because of this, men who have sex with men have a high risk of this cancer.

Smoking

Smoking increases the risk of anal cancer. Current smokers are several times more likely to have cancer of the anus compared with people who do not smoke. Quitting smoking seems to reduce the risk. People who used to smoke but have quit are only slightly more likely to develop this cancer compared with people who never smoked.

Lowered immunity

Higher rates of anal cancer occur among people with reduced immunity, such as people with AIDS or people who have had an organ transplant and must take medicines that suppress their immune system.

Gender and race/ethnicity

Anal cancer is more common in women than men overall, but this varies in racial/ethnic groups and can vary with age. For instance, in African Americans younger than age 60, it's more common in men than in women, but after age 60 it's more common in women.