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Risks and causes

Your risk of developing anal cancer depends on many things, including age and lifestyle factors. Having HPV is the biggest risk factor for anal cancer. Most of us have HPV at some point during our life. But for most people it won't cause anal cancer. 

Anything that can increase your risk of cancer is called a risk factor. Those that lower the risk are called protective factors.

Having one or more risk factors doesn’t mean that you will definitely get anal cancer.

Human papilloma virus (HPV)

Men and women with HPV have an increased risk of developing anal cancer. Around 90 in 100 cases of anal cancer (around 90%) are linked to HPV infection. 

HPV is a common infection that gets passed from one person to another by sexual contact. For most people the virus causes no harm and goes away without treatment. 

Types of HPV

There are many different types of HPV, most are harmless, some cause genital warts, and others can cause cancer. 

Of the different types of HPV, type 16 is the most common in anal cancer. 

Sex

People who have anal intercourse may 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.

Vaccines

There are now vaccines to prevent HPV infection. All girls and boys aged 12 or 13 in the UK are routinely offered the HPV vaccine at school. 

These vaccines protect against the types of HPV that are most likely to cause cancers such as cervical and anal cancer. They don’t protect against all types of HPV.

HPV vaccination works better in people who haven’t ever had an HPV infection. As HPV is mostly passed on through sexual contact, the vaccination programme is offered at a young age when people are less likely to have had sexual experiences.

Men who are 45 or under and have sex with men are able to have the HPV vaccine on the NHS when they go to a sexual health clinic or HIV clinic.

Age and gender

Your risk of developing anal cancer increases as you get older.

Around 25 out of 100 people (around 25%) diagnosed with anal cancer each year in the UK are aged 75 and over. But as anal cancer is a rare cancer the risk is still small.

Anal cancer is more common in women than men.

Human Immunodeficiency Virus (HIV)

Having the human immunodeficiency virus (HIV) increases your risk of developing anal cancer. 

Smoking

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

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 higher for women with a history of abnormal cells in the cervix, vulva or vagina.

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 anal cancer risk.

Other possible causes

Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.

For more detailed information about risks and causes

Last reviewed: 
24 Jan 2020
  • Anal cancer risk factors
    Statistical Information Team at Cancer Research UK

  • International Agency for Research on Cancer. List of Classifications by cancer sites with sufficient or limited evidence in humans
    Volumes 1 to 122 
    Accessed August 2018.

  • The fraction of cancer attributable to known risk factors in England, Wales, Scotland, Northern Ireland, and the UK overall in 2015
    KF Brown and others
    British Journal of Cancer 2018. 

  • The epidemiology of anal cancer
    AE Grulich and others
    Sexual Health. 2012 Dec;9(6):504-8

  • Anal Cancer: ESMO-ESSO-ESTRO Clinical Practice Guidelines
    R. Glynne-Jones and others
    Annals of Oncology, 2014: 25 (suppl 3): iii10-iii20

  • Second cancers among 104,760 survivors of cervical cancer: evaluation of long-term risk.
    AK Chaturvedi AK and others
    J Natl Cancer Inst 2007;99:1634-43.

  • Risk of anal cancer in a cohort with human papillomavirus-related gynecologic neoplasm.
    AM Saleem and others
    Obstet Gynecol. 2011 Mar;117(3):643-9.

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in if you need additional references for this information.

     

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