Anal cancer is a rare cancer that starts in the anus. This is the opening at the very end of the large bowel.
The anus is the part of the large bowel that opens to the outside of the body. It is the tube that your stools pass through as you empty your bowels. It is also called the anal canal. It is about 3 cm long, and is at the end of your rectum.
Parts of the anus
The anal canal connects the anus to the rectum.
The anal margin is the lower part of the anal canal. The anal margin contains muscles called the anal sphincters. The external anal sphincter is the muscle you use to control your bowel movements.
The transitional zone is higher up, where the anal canal meets the rectum.
Where it starts
Anal cancer can start in any part of the anus. Anal margin tumours are more common in men than women. Cancers that start higher up in the anal canal are more common in women.
Cancers of the anal margin usually look more like normal cells. Doctors call these well differentiated tumours.
There are different types of anal cancer. Your type depends on which type of cell the cancer starts in. This can affect what treatment you have.
Most anal cancers start in squamous cells that make up the lining of the anal canal. These are called squamous cell cancers.
The lining of the transitional zone is made up of both squamous and glandular cells. Glandular cells make the mucus that helps stools (faeces) pass through the anus smoothly. Rarely, anal cancer can develop from the glandular cells. This is called adenocarcinoma of the anus.
Melanoma is another rare type of anal cancer. It starts in cells in the skin called melanocytes.
How common it is
Anal cancer is a rare cancer. In 2015, around 1,500 people were diagnosed in the UK. That’s around 4 cases diagnosed every day in the UK.
The number of people in the UK diagnosed with anal cancer has been increasing. There is a larger increase for women than men.
Who gets it
Anal cancer is more common in women than men. And it is more common in older people.
Many anal cancers are linked to lifestyle or other risk factors. The main risk factor for anal cancer is human papilloma virus (HPV) infection. HPV is linked to around 9 in 10 cases (90%) f anal cancer in the UK.