What is anal cancer?
Anal cancer is cancer affecting the tissues of the anus, the opening at the end of the bowel.
About the anus
The anus is made up of the last few centimetres of the bowel (anal canal) and the skin around the opening (anal margin). During a bowel movement, the muscles of the anus (sphincters) relax to release the solid waste matter known as faeces or stools.
Structure of the anus
Types of anal cancer
- Squamous cell carcinomas (SCCs) – Most anal cancers are squamous cell carcinomas (SCCs). These start in the flat (squamous) cells lining much of the anus. The term “anal cancer” commonly refers to SCCs, and this fact sheet focuses on this type of anal cancer.
- Adenocarcinomas – Some anal cancers are adenocarcinomas. These start in cells in the anal glands. This type of anal cancer is similar to bowel cancer and is treated in a similar way. See Bowel cancer for more information.
- Skin cancers – In rare cases, SCCs can affect the skin just outside the anus. These are called perianal skin cancers. If they are not too close to the sphincters, they can be treated in a similar way to SCCs on other areas of skin. See Skin cancer for more information.
Who gets anal cancer?
Every year, about 430 people are diagnosed with anal cancer in Australia. It is more common over the age of 50 and is somewhat more common in women than in men. The number of people diagnosed with anal cancer is increasing, with four times more cases in 2014 than in 1984.
What causes anal cancer?
About 80% of anal cancers are caused by a very common infection called human papillomavirus (HPV). HPV can affect the surface of different areas, including the anus, cervix, vulva, vagina and penis. Unless they are tested, most people won’t know they have HPV as it usually doesn’t cause symptoms. HPV is the main risk factor for anal cancer, but other factors that may increase the risk include:
- having a weakened immune system, e.g. because of human immunodeficiency virus (HIV), an organ transplant or an autoimmune disease such as lupus
- having anal warts
- being a man who has had sex with other men
- being a woman who has had an abnormal cervical Pap test or cancer of the cervix, vulva or vagina
- being over 50.
However, some people with anal cancer do not have any of these risk factors.