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Risks and causes of anal cancer

Men and women discussing anal cancer

This page is about the possible causes of anal cancer. You can go straight to sections about

 

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Risks and causes of anal cancer

Anal cancer is rare. It is slightly more common in women than men. We don’t know the cause of anal cancer but there are several risk factors.

Human papilloma virus (HPV)

There are over 100 different types of HPV. Some types are passed on from one person to another through sexual contact. About 9 out of 10 people (90%) diagnosed with anal cancer have evidence of HPV infection.

Other risk factors

Apart from getting older, other possible risk factors include having had cancer or abnormal cells of the cervix, vagina or vulva in the past, smoking and a lowered immunity.

 

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How common anal cancer is

Anal cancer is a rare cancer. Just under 1,200 people are diagnosed each year in the UK. It is more common in women than men, with rates increasing over the past 10 years. We don’t know the cause of anal cancer but there are several risk factors.

 

What risk factors are

Anything that increases your risk of getting a disease is a risk factor. Different cancers have different risk factors. Even if you have more than one risk factor it doesn’t mean you will definitely get the disease. And just because researchers investigate a possible cause, that doesn't mean it will turn out to be a risk factor.

 

Human papilloma virus (HPV)

There are more than 100 different types of human papilloma virus (HPV). Some types are called the wart virus or genital wart virus as they cause genital warts. Other types have been linked with certain cancers, such as cervical cancer. Some types of HPV are passed on from one person to another through sexual contact.

Most sexually active adults will be infected with at least one type of HPV at some time during their life. For many people, the virus causes no harm and goes away without treatment.

People who have had a greater number of sexual partners may be more likely to have HPV. Some studies show that people who have other sexually transmitted infections may be more likely to have HPV. Men who have anal intercourse may also have a higher risk of HPV.

Around 9 in 10 cases of anal cancer (90%) are linked to HPV infection. Of the different types of HPV, type 16 is the most common in anal cancer. Invasive anal cancer is thought to develop from the growth of abnormal cells (squamous intraepithelial lesions) caused by HPV infection.

If you have a history of genital warts you have an increased risk of anal cancer. People who have anal intercourse or who have a greater number of sexual partners may also have an increased risk of anal cancer. This could be due to the increased risk of HPV infection. Using condoms every time you have sex can lower your chances of getting HPV. But HPV can infect areas that are not covered by a condom so they don't reduce the risk completely.

 

History of cervical, vaginal or vulval cancer

Some studies show that if you have had cervical, vulval or vaginal cancer you have a higher risk of developing abnormal cells in the anus or anal cancer than the general population.The risk is also increased for women with a history of abnormal cells in the cervix (cervical intraepithelial neoplasia), vulva (vulval intraepithelial neoplasia) or vagina (vaginal intraepithelial neoplasia). This is probably due to risk factors common to all these cancers, such as HPV infection. But we need more research to fully understand how these cancers affect the risk of anal cancer.

 

Smoking

Some studies have shown smoking increases the risk of cancer of the anus. Giving up smoking can reduce your risk of developing many cancers.

 

Lowered immunity

If you have lowered immunity you are at greater risk of developing anal cancer compared to the general population. You have an increased risk if you have HIV. Anal cancer is generally diagnosed at a younger age among people with HIV. This is even taking into account that HIV is more common in younger people.

People taking medicines to damp down their immune system after an organ transplant (for example, a kidney transplant) also have an increased risk of anal cancer.

 

Age

Your risk of developing anal cancer increases as you get older. But the risk is still small because anal cancer is a rare cancer.

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Updated: 5 February 2014