Overview

Anal cancer begins when normal cells in or on the anus begin to change and grow uncontrollably, forming a mass called a tumor. A tumor of the anus can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other areas of the body). There are also growths that can occur in or around the anus, such as polyps or warts. While these growths are not cancerous, some may become cancerous over time.

The anus is part of the gastrointestinal tract and is the opening at the end of the large intestine, below the rectum, where bowel movements leave the body. The anus is made up of different types of cells, and each type can become cancerous. There are several different types of anal cancer based on the type of cell where the cancer began:

• Squamous cell carcinoma is the most common type of anal cancer. This cancer begins in the outer lining of the anal canal.
  
  
• Cloacogenic carcinoma accounts for about one-quarter of all anal cancers. This cancer arises between the outer part of the anus and the lower part of the rectum. Cloacogenic cell cancer likely starts from similar cells as squamous cell cancer and is treated similarly.
  
  
• Adenocarcinoma arises from the glands that make mucous, located under the anal lining.
  
  
• Basal cell carcinoma is a type of skin cancer that can appear in the perianal (around the anus) skin.
  
  
• Melanoma begins in cells in the skin or anal lining that darken the skin.

Statistics

In 2009, an estimated 5,290 adults (2,100 men and 3,190 women) in the United States will be diagnosed with anal cancer. It is estimated that 710 deaths (260 men and 450 women) from this disease will occur this year.

The overall five-year relative survival rate (percentage of people who survive at least five years after the cancer is detected, excluding those who die from other diseases) of people with anal cancer is 66%. The five-year survival rate of people with cancer that has not spread is 80%. The five-year relative survival rate for tumors that have spread to the area around the anus and those that have spread to more distant body parts is 61% and 29%, respectively. The five-year relative survival rate may be lower for people who have human immunodeficiency virus (HIV), the virus that causes acquired immune deficiency syndrome (AIDS).

Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States each year, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with anal cancer. Because the survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.

Statistics adapted from the American Cancer Society's publication, Cancer Facts & Figures 2009, and the National Cancer Institute Surveillance Epidemiology and End Results (SEER) database. 

Find out more about basic cancer terms used in this section.