What is Anal Cancer?

Anal cancer is cancer that forms in the cells that line your anus. There are about 8,000 new cases of anal cancer in the United States each year. With the HPV vaccination available, it is expected for this trend to start decreasing in the coming decades. The anus is an approximately 1 1/2 inch canal that leads from your rectum (the last section of your large intestine) to the outside of your body. The anus has two ring-like sphincter muscles that open and close to let waste (stool) leave the body. Your anus is lined with squamous cells, which are thin, flat cells that are also found in many other parts of the body such as the skin. Thus, >90% of anal cancers are squamous cell carcinomas, which form in cells just inside the opening of the anus. Some anal cancers may also be adenocarcinomas, which form in the glandular tissues around the anal canal, or in the upper part of the anus near the rectum. Adenocarcinomas are much less common and are treated more like rectal cancer, so this page focuses primarily on squamous cell carcinomas.