Questions About Cancer? 1-800-4-CANCER
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Anal Cancer Prevention (PDQ®)

General Information About Anal Cancer

Anal cancer is a disease in which malignant (cancer) cells form in the tissues of the anus.

The anus is the end of the large intestine, below the rectum, through which stool (solid waste) leaves the body. The anus is formed partly from the outer skin layers of the body and partly from the intestine. Two ring-like muscles, called sphincter muscles, open and close the anal opening and let stool pass out of the body. The anal canal, the part of the anus between the rectum and the anal opening, is about 1-1½ inches long.

Gastrointestinal (digestive) system anatomy; shows esophagus, liver, stomach, colon, small intestine, rectum, and anus.
Anatomy of the lower digestive system, showing the colon and other organs.

The skin around the outside of the anus is called the perianal area. Tumors in this area are skin tumors, not anal cancer.

See the following PDQ summary for more information about anal cancer:

Squamous cell carcinoma is the most common type of anal cancer.

In the United States, the most common type of anal cancer is squamous cell carcinoma. Studies show that human papillomavirus (HPV) infection is the main cause of this type of anal cancer.

Another type of anal cancer, called anal adenocarcinoma, is very rare and is not discussed in this summary.

In the United States, the number of new cases of anal cancer has increased in recent years.

From 2001 to 2010, new cases of anal cancer and deaths from anal cancer increased each year. The increase in new cases was slightly higher in women and the increase in deaths from anal cancer was slightly higher in men.

  • Updated: December 11, 2014