Anal cancer causes and risk factors

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on June 8, 2022.

Each year, more than 9,700 people in the United States are diagnosed with anal cancer. No one knows whether or when this disease will develop, but knowing the risk factors for anal cancer may help people take preventive measures to reduce the likelihood of developing this disease.

What causes anal cancer?

Human papillomavirus (HPV), a collection of more than 150 viruses spread primarily by contact during vaginal, oral or anal sexual activity, is responsible for the majority of anal cancers.

Anal cancer develops when cells located in the anus mutate (or change) and begin to grow out of control, forming a tumor. In some cases, these altered cells die or are attacked by the immune system. But some cells may escape the immune system and grow out of control, and they may then develop into a tumor.

Anal cancer risk factors

Known risk factors for anal cancer include the following.

Anal HPV

Chronic infection with high-risk types of HPV is the most significant risk factor for anal cancer.

HPV may be asymptomatic for years, and persistent HPV infections may cause cell changes that, left untreated, may become cancer. The HPV vaccine provides protection against numerous strains of the virus, including subtypes 16 and 18, which are responsible for most HPV-related cancers.

Patients with a history of anal warts also have an increased risk of anal cancer. This is due to the fact that people with anal warts are more likely to have an HPV infection.

Anal sex and cancer

Men and women with a history of receptive anal intercourse, especially those younger than 30, have a higher risk of anal cancer.

Other risk factors for anal cancer

Other potential risk factors for anal cancer include those listed below.

HIV infection: People with the human immunodeficiency virus (HIV), which causes AIDS, are more likely to develop anal cancer.

Some gynecologic cancers: Women with a history of cervical, vulvar or vaginal cancer, which are also are caused by HPV infection, have an increased anal cancer risk.

Lowered immunity: Having a compromised immune system means an increased risk for developing anal cancer. For example, people who have had an organ transplant and take medicines to suppress their immune system or are receiving chemotherapy for another type of cancer.

Chronic local inflammation: Those with anal fistulas or open wounds that last a long time, have a slightly higher risk for developing anal cancer.

Age: Two-thirds of anal cancer cases occur in people older than 55.

Smoking: Smokers have a significantly higher risk for developing anal cancer. The risk greatly decreases when smokers quit.

Race and gender: Incidence of anal cancer is higher among African Americans, particularly men, than in whites. Women are also at greater risk than men for the disease.

Anal cancer prevention

While it’s impossible to completely eliminate the risk for developing cancer, knowing the risk factors for anal cancer is key to taking steps to help prevent the disease. Avoid unprotected anal sex, and use condoms to reduce the risk of HPV and HIV infection. People who smoke should quit, and those who don’t smoke should avoid picking up the habit.

Next topic: What are the symptoms of anal cancer?

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