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 (HPV) 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. In general, anal cancer develops more often in women than in men. But black men have a higher rate of anal cancer than white men and black women.

Precancerous conditions of the anus include anal intraepithelial neoplasia (AIN). AIN isn’t cancer, but it can sometimes become anal cancer if it isn’t treated. Some of the risk factors for anal cancer may also cause this precancerous condition. Find out more about precancerous conditions of the anus.

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.

Risk factors

Human papillomavirus (HPV) infection

Sexual behaviour

Weakened immune system

History of cervical, vaginal or vulvar cancer

Smoking tobacco

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

Human papillomavirus (HPV) infection

HPV infection is found in about 90% of people with anal cancer. There are several subtypes of the virus, but HPV16 and HPV18 are most likely to cause anal cancer. 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 sexual 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).

Sexual behaviour

In both men and women, some sexual activities increase the risk for 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 compared to the overall male population.

Weakened immune system

People with 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 a weakened immune system may not be able to get rid of an HPV infection, which can eventually lead to cancer.

History of cervical, vaginal or vulvar cancer

Women who have been diagnosed with cancer of the cervix, vagina or vulva have a higher 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.

Smoking tobacco

Studies show that smoking tobacco increases the risk for anal cancer. Smokers are several times more likely to have anal cancer compared with people who don’t smoke.

No link to anal cancer

Significant evidence shows no link between non-cancerous tumours of the anus and a higher risk for anal cancer.

Questions to ask your healthcare team

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

immunosuppression

Suppression of the body’s immune system so it is less able to fight infections or diseases.

Immunosuppression can be caused by certain diseases, such as AIDS or lymphoma. It may also be a side effect of certain chemotherapy drugs. Doctors may also deliberately suppress the immune system before organ or stem cell transplants to prevent rejection.

Also called immunocompromised.

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