Causes and risk factors of anal cancer
There are some risk factors that can increase your chance of developing anal cancer. Most anal cancers are caused by the human papillomavirus (HPV).
What are the risk factors of anal cancer?
In the UK, about 1,500 people develop anal cancer each year. It is a rare cancer. But the number of people being diagnosed with anal cancer is increasing – especially women. Anal cancer is much more common in women and people assigned female at birth than in men and people assigned male at birth.
Anal cancer can also affect trans and non-binary people. If you are transgender (trans) or non-binary, you might find our web page for LGBTQ+ people affected by cancer helpful.
Risk factors can increase the chance of a person developing a certain type of cancer. Having 1 or more risk factor does not mean you will definitely get anal cancer. If you do not have any risk factors, it does not mean you will not get anal cancer.
Most anal cancers are caused by the human papillomavirus (HPV).
Bowel cancer is a general term for a cancer that starts in either the colon or the rectum.
We have separate information about:
If you are worried about anal cancer and would like to talk to someone, we are here. You can:
- call the Macmillan Support Line for free on 0808 808 00 00.
- chat to our specialists online
- visit our anal cancer forum to talk with people who have been affected by anal cancer, share your experience, and ask an expert your questions.
Human papilloma virus (HPV)
HPV is a virus that is linked to different cancers, including anal cancer. It is a common virus that is passed on through sexual contact. Most people have HPV at some point and never know they have had it.
There are over 100 types of HPV. Some types are more likely to cause cancer than others. Some types may cause genital warts. The types of HPV usually linked to anal cancer are HPV16 and HPV18. Using a condom might help to reduce the risk of getting HPV.
The immune system usually gets rid of HPV without it causing any problems. But a small number of HPV infections eventually lead to cancer developing. If you smoke or have a weakened immune system, your body may find it harder to get rid of HPV.
HPV vaccination is expected to reduce the number of people diagnosed with anal cancer. The HPV vaccine is recommended for children aged 12 to 13 years old and people at higher risk of HPV.
We have more information about HPV and cancer. This includes information about HPV testing and vaccination if you have a higher risk of developing anal cancer. If you are worried, talk to your GP or local sexual health clinic for more information.
Sexual activity
Although HPV can be passed on through any type of sexual contact, certain sexual activities increase the risk of anal cancer. This includes receiving anal sex. But HPV can be passed on in different ways.
Men who have sex with men have a higher risk of anal cancer than other men. This includes trans women and other people assigned male at birth who have sex with men.
HIV
Organ transplant and reduced immunity
People taking medicines to suppress their immune system after an organ transplant have a higher risk of anal cancer. This is because they have a weakened immune system (reduced immunity).
Smoking
Smoking tobacco increases the risk of developing anal cancer. If you are diagnosed with anal cancer, stopping smoking has lots of benefits. Your doctor or nurse will talk to you about this.
Age
Like most types of cancer, the risk of developing anal cancer increases as you get older. About one quarter of people diagnosed with anal cancer (25%) are 75 and over. But much younger people can also be affected.
Sex
Anal cancer is much more common in women than in men. This includes trans men and other people assigned female at birth.
Anal intraepithelial neoplasia (AIN)
This is when abnormal cells develop in the skin just inside or outside the anus. It is usually caused by the same types of HPV that cause anal cancer. Most people who have AIN have no symptoms. But symptoms can include:
- itching or irritation around the anus
- bleeding in the area
- feeling you need to poo without being able to (tenesmus).
There are different grades of AIN. Low-grade AIN does not usually develop into cancer. But if high-grade AIN is left untreated, it can develop into cancer over many years.
The Anal Cancer Foundation has more information on AIN and how it should be screened or monitored.
Precancerous cells in the cervix or vulva
HPV infection can also cause abnormal changes in the cells of the cervix or vulva. These are not cancer, but if not treated over time they may develop into cancer.
You may have a higher risk of anal cancer if you have had:
- abnormal cells in the cervix – this is called cervical intraepithelial neoplasia (CIN)
- abnormal changes in the cells of the vulva – this is called vulval intraepithelial neoplasia (VIN).
Other cancers linked to HPV
People who have had another cancer linked to HPV have an increased risk of anal cancer. These include:
Warts
About our information
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer.
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References
Below is a sample of the sources used in our anal cancer information. If you would like more information about the sources we use, please contact us at informationproductionteam@macmillan.org.uk
S Rao, MG Guren, K Khan et al. Anal cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. 2021. European Society of Medical Oncology. Available from: www.esmo.org/guidelines/guidelines-by-topic/esmo-clinical-practice-guidelines-gastrointestinal-cancers/anal-cancer [accessed January 2023].
O Dahl, MP Myklebust, JE Dale et al. Evaluation of the stage classification of anal cancer by the TNM 8th version versus the TNM 7th version. 2020. Acta Oncologica, 59(9), 1016–1023. Available from: www.tandfonline.com/doi/full/10.1080/0284186X.2020.1778180 [accessed December 2022].
Date reviewed
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The language we use
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We want our information to be as clear as possible. To do this, we try to:
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We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.
You can read more about how we produce our information here.
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