Anal Cancer is a rare disease, affecting around 1300 people a year in the UK (Cancer Research UK). It is slightly more common in women than in men, with a male:female ratio of cases of 1:2. The outlook for anal cancer is often better than for other types of bowel cancer, especially when caught in the earlier stages.
The anus (back passage) is the 4cm long end portion of the large bowel, which opens to allow solid waste to exit the body. Abnormal changes of the anus are sometimes harmless in their early stages, but may go on to develop into cancer. Different cancers can develop in different parts of the anus. Types of anal cancer include:
The most common type of anal cancer (about 75% of cases) is squamous cell carcinoma, which starts in the cells lining the anal margin and the anal canal. The anal margin is the edge of the anus that can be partly seen as darker skin on the outside of the body and the anal canal is the part of the anus that is inside the body. The earliest stage of squamous cell carcinoma is known as carcinoma in situ, or Bowen’s disease.
An estimated 15% of anal cancers are called adenocarcinoma. These affect glands in the anal area and one type of adenocarcinoma that can occur in the anal area, known as Paget’s disease, can also affect the vulva, breasts, and other areas of the body. Anal adenocarcinomas are usually treated in the same way as rectal cancer.
A small number of anal cancers are either basal cell carcinomas, or malignant melanomas – two different types of skin cancer.
Other, very rare types of anal cancer are lymphomas, and gastrointestinal stromal tumours (GIST).