Anal Cancer

The anus is the name for the muscular opening at the very end of the large bowel.

It is controlled by a ring of muscle called a sphincter that opens and closes to control bowel movements. The area that connects the anus to the rectum is called the anal canal and is around 3–4cm (1–1½in) long (see diagram below).

Cancer of the anus is rare. Around 930 people are diagnosed with anal cancer each year in the UK.

The most common type of anal cancer is squamous cell carcinoma. Other rarer types are basal cell carcinoma, adenocarcinoma and melanoma. This information is about squamous cell carcinoma.



Causes and possible risk factors

Anal cancer is slightly more common in women than men. There are a number of factors that can increase your risk of developing anal cancer. These include:

Human papilloma virus (HPV)
Anal cancer is more likely to develop in people who have had a viral infection called thehuman papilloma virus (HPV). The risk of having HPV increases with the number of sexual partners you have.

Sexual activity
People who have anal intercourse are more likely to develop anal cancer. This may be because they are more likely to have anal HPV.

Lowered immunity
The immune system is part of the body's defence against infections and illnesses like cancer.

Anal cancer is more common in people who have a lowered immunity, such as people taking medicines to suppress their immune system after an organ transplant or people with conditions such as HIV.

Smoking
Smoking tobacco increases the risk of developing anal cancer. We have more information on stopping smoking.

However, many people who get anal cancer will not have these risk factors and the cause remains unknown.