Anal cancer is a type of cancer that forms in the tissues of the anus.
The anus is the end of the large intestine. It is where feces (solid waste) leaves the body. The anus is made up partly of the outer layers of skin on the body and partly of the intestine. The anus is connected to the rectum by the anal canal, which is about 1 to 1½ inches long. This area is controlled by two ring-shaped sphincter muscles, which contract to retain stool and relax to allow it to exit the body.
Anal cancer can start in the lining of the anal canal, called mucosa, or in the perianal skin, the squamous cells outside the anus that contain hair follicles and sweat glands.
Perianal skin tumors that do not affect the anal sphincter are usually treated in the same way as anal cancers, although local therapy (treatment directed at a limited area of skin) may be used in some cases.
Squamous cell carcinoma is the most common type of anal cancer. In the United States, squamous cell carcinoma is the most common type of anal cancer. 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.
