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 motion, the muscles of the anus (sphincters) relax to release the solid waste matter known as faeces or stools.
Anal cancer is cancer affecting the tissues of the anus. Cancer is a disease of the cells, the body’s basic building blocks. Our body constantly makes new cells to help us grow, replace worn-out tissue and heal injuries. Normally cells multiply and die in an orderly way.
When cells don’t grow, divide and die in the usual way, they sometimes form a lump called a tumour. If the cells are cancerous, they can spread through the bloodstream or lymph fluid and form another tumour at a new site. This new tumour is known as secondary cancer or metastasis.
Most anal cancers are squamous cell carcinomas (SCCs), which come from the flat (squamous) cells that line much of the anus. The term ‘anal cancer’ commonly refers to these SCCs, and this page focuses on this type of anal cancer.
A small number of anal cancers are adenocarcinomas, which start from cells in the anal glands. This type of anal cancer is similar to bowel cancer and is treated in a similar way. See our bowel cancer section for more information.
A very small number of anal cancers affect the skin just outside the anus. Known as perianal skin cancers, they are treated in a similar way to skin cancers that are found on other parts of the body. See our skin cancer section for more information.
Every year, about 400 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. However, men who have sex with men have the highest incidence of any group. The number of people diagnosed with anal cancer is increasing, with three times more cases in 2011 than in 1984.
About 80% of anal cancer cases are caused by a very common infection called human papillomavirus (HPV). HPV can affect the surface of different areas of the body, including the anus, cervix, vagina and penis. Most people will not be aware that they have HPV as it usually doesn’t cause any symptoms.
Other factors that increase the risk of getting anal cancer include:
In its early stages, anal cancer often has no obvious symptoms. However, some people may experience symptoms such as:
Not everyone with these symptoms has anal cancer. Other conditions, such as haemorrhoids or tears in the anal canal (anal fissures), can also cause these changes. However, if the symptoms are ongoing, see your general practitioner (GP) for a check-up.
The main tests for diagnosing anal cancer are:
Your doctor inserts a gloved finger into your anus to feel for any lumps or swelling. This is called a digital anorectal examination (DARE).
A small, rigid instrument called a proctoscope is inserted, with lubricant, into the anus to see the lining of the anal canal. This may be done under a local or general anaesthetic so that a tissue sample (biopsy) can be taken at the same time. The biopsy will be sent to a laboratory for testing.
If anal cancer is diagnosed, you will have further tests to check whether it has spread. Most people will have a colonoscopy, which is an examination of the large bowel (colon). You may also need one or more imaging scans, such as an MRI, an endorectal ultrasound, a CT scan or an FDG-PET scan. To find out more about these tests call Cancer Council 13 11 20.
Staging describes how far the cancer has spread. Knowing the stage helps doctors plan the best treatment for you. Anal cancer is staged using the TNM (Tumour Nodes Metastasis) system.
Indicates how far the tumour has grown into the bowel wall and nearby areas. T1 is a smaller tumour; T4 is a larger tumour.
Shows if the cancer has spread to nearby lymph nodes (small glands). N0 means no cancer is in the lymph nodes; N1 means cancer is in the lymph nodes around the rectum; N2 means cancer is in pelvic and/or groin lymph nodes on one side; N3 means cancer is in pelvic and groin lymph nodes on both sides.
Shows if the cancer has spread
to other, distant parts of the body.
M0 means cancer has not spread;
M1 means cancer has spread.