Anal cancer is cancer affecting the tissues of the anus, the opening at the end of the bowel.
Learn more:
About the anus
The anus is the opening at the end of the bowel. It 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, stools or poo.
Structure of the anus
Types of anal cancer
| squamous cell carcinoma (SCC) | Most anal cancers are SCCs. These start in the flat (squamous) cells lining much of the anus. The term “anal cancer” commonly refers to SCCs, and here we focus on this type of anal cancer. |
| adenocarcinoma | Some anal cancers are adenocarcinomas. These start in cells in the anal glands. This type of anal cancer is treated in a similar way to bowel cancer. |
| skin cancer | 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 sphincter muscles, they can be treated in a similar way to SCCs on other areas of the skin. For more on this, see Skin cancer. |
Who gets anal cancer?
Every year, about 460 people are diagnosed with anal cancer in Australia. It is more common over the age of 50 and is slightly more common in women than in men. The number of people diagnosed with anal cancer has increased over recent decades.
What causes anal cancer?
About 80% of anal cancers are caused by infection with a very common virus called human papillomavirus (HPV). HPV can infect the surface of different areas, including the anus, cervix, vulva, vagina, penis, mouth and throat. Unless they are tested, most people won’t know they have HPV infection as it usually doesn’t cause symptoms.
HPV infection 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) infection, an organ transplant, or an autoimmune disease such as coeliac disease, lupus or Graves’ disease
- being a man who has had sex with other men
- having anal warts
- having had an abnormal cervical screening test or cancer of the cervix, vulva or vagina
- smoking tobacco
- being aged over 50.
Some people with anal cancer do not have any of these risk factors.
→ READ MORE: Anal cancer symptoms
More resources
Dr Chip Farmer, Colorectal Surgeon, The Alfred, The Avenue and Cabrini Hospitals, VIC; Tara Faure, Lower GI Nurse Consultant, Peter MacCallum Cancer Centre, VIC; Dr Debra Furniss, Radiation Oncologist, GenesisCare, QLD; Caitriona Nienaber, 13 11 20 Consultant, Cancer Council WA; Max Niggl, Consumer; Julie O’Rourke, CNC Radiation Oncology, Cancer Rapid Assessment Unit, Cancer and Ambulatory Support, Canberra Health Services ACT; Dr Satish Warrier, Colorectal Surgeon, Peter MacCallum Cancer Centre, VIC.
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