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Anal cancer

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Risk factors for anal cancer

A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors. Human papillomavirus infection is the most important risk factor for anal cancer.

The risk of developing anal cancer increases with age. It is usually seen in people over the age of 55. Black men have a higher rate of anal cancer than white men and black women. In most other people, anal cancer is seen more often in women than in men.

The following are risk factors for anal cancer. Risk factors are generally listed in order from most to least important. But in most cases, it is impossible to rank them with absolute certainty.

Significant evidence shows no link between benign anal conditions and anal cancer.

Known risk factors

There is convincing evidence that the following factors increase your risk for anal cancer.

Human papillomavirus (HPV) infection

HPV infection has been strongly linked to anal cancer and is found in about 90% of anal cancers. There are several subtypes of the virus, but the ones most likely to cause anal cancer are HPV-16 and HPV-18. HPV infection can also cause cervical, vaginal, vulvar, penile and some oral cavity and oropharyngeal cancers.

Infection with HPV is common. In most cases, a person’s healthy immune system will clear the infection on its own. But in some cases, the infection does not go away and can eventually cause certain cancers, including anal cancer.

HPV is easily passed from one person to another through skin-to-skin contact with an area of the body infected with HPV. A person can become infected with HPV without having sexual intercourse. An HPV infection can spread from one part of the body to another. For example, the infection may start in the genitals and then spread to the anus.

Learn more about human papillomavirus (HPV).

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Sexual behaviour

In both men and women, some sexual activities increase the risk of anal cancer. These activities include having receptive anal intercourse (receiving anal sex) and having many sexual partners. There are higher rates of anal cancer among men who have sex with men (homosexual men) compared to the general male population.

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Weakened immune system

People with lowered immunity (immunosuppression) seem to have higher rates of anal cancer. This includes people with a human immunodeficiency virus (HIV) infection and those who have had an organ transplant and must take medicines to suppress their immune system.

The role of immunosuppression in anal cancer is not entirely clear. It is thought that lowered immunity may allow for a persistent HPV infection (an HPV infection that doesn’t go away) to develop and eventually lead to cancer.

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History of cervical, vaginal or vulvar cancer

Women who have been diagnosed with cancer of the cervix, vagina or vulva have an increased risk of developing anal cancer. This may be because these cancers have similar risk factors, such as an HPV infection.

Find out more about cervical cancer, vaginal cancer and vulvar cancer.

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Possible risk factor

Smoking

Some studies suggest that smoking may be a risk factor for anal cancer.

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Questions to ask your healthcare team

To make the decisions that are right for you, ask your healthcare team questions about risks.

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