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A risk factor is anything that increases 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, cannot.

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 will never develop anal cancer, while others with this disease may have few or no known risk factors.

HPV (human papillomavirus) infection

Infection by the human papillomavirus (HPV) is the most important risk factor for anal cancer. Most squamous cell anal cancers are linked to infection with HPV. HPV is a group of more than 150 related viruses, the same group of viruses that causes cervical cancer, as well as other kinds of cancer. In fact, women with a history of cervical cancer (or pre-cancer) have an increased risk of anal cancer.

• HPV can infect cells on the surface of the skin, and those lining the genitals, anus, mouth and throat, but not the blood or internal organs such as the heart or lungs.
• HPV can spread from one person to another during skin-to-skin contact. One way HPV spreads is through sexual activity, including vaginal, anal, and even oral sex.
• Different types of HPV cause warts on different parts of the body. Some cause common warts on the hands and feet; others tend to cause warts on the lips or tongue.

Infection with HPV is common, and in most cases, the body can clear the infection by itself. Sometimes, however, the infection does not go away and becomes chronic. Chronic infection, especially when it is caused by certain high-risk HPV types, can eventually cause certain cancers, such as anal cancer.

Certain types of HPV are called high-risk because they are strongly linked to cancers including anal cancer, as well as cancer of the cervix, vulva, and vagina in women, penile cancer in men, and cancers of the anus, mouth, and throat in both men and women. The high-risk subtype most likely to cause anal cancer is HPV-16. Another high-risk type is HPV-18, but this is seen less often with anal cancer.

Other types of HPV may cause warts in or around the anal area and on the female and male genital organs. These are called low-risk types of HPV because they are seldom linked to cancer.

Although there is currently no cure for HPV infection, there are ways to treat the warts and abnormal cell growth that HPV causes. Also, HPV vaccines are available to help prevent infection by certain types of HPV and some of the cancers linked to those types.

Anal warts

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 with HPV subtypes that cause anal cancer.

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.

HIV infection

People infected with HIV (the human immunodeficiency virus), the virus that causes AIDS, are much more likely to get anal cancer than those not infected with this virus. For more information 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. The higher a person's pack-year history of smoking, the higher their risk of developing anal cancer.  People who currently smoke are more likely to have cancer of the anus compared with people who do not smoke or have quit smoking. Quitting smoking seems to reduce the risk.

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.

Sex and race/ethnicity

Anal cancer is more common in White women and Black men.