The Anus is the lower part of the gastrointestinal tract and is attached to the rectum. It is the opening through which stool passes out of the body. It is approximately 3-4 cm long. This has a complex anatomy as the skin on the outside of the body is completely different than the mucosa which lines the bowel. The area where the two different types of tissue change places is called the dentate line. The anal sphincter is a series of delicate muscles that serve to control the passage of stool, and often these muscles are damaged by anal cancer.l.
Anal cancer is fairly uncommon. Approximately 8080 people are diagnosed with anal cancer each year in the United States. More than 80% of anal canal tumors occur in individuals older than 60 years. The Anal cancer accounts for approximately one tenth of the rectal cancers and only 3% of bowel cancer in general. Anal cancer seems to be increasing in developed countries, likely related to lifestyle factors. Early stage anal cancer is increasing at a faster rate. Scientists have noted that anal cancer is quite different than rectal or colon cancer and that the things that predispose to large bowel cancer do not normally increase the risk of anal cancer.
The number of cases of anal cancer diagnosed each year has been increasing over the last 10 years. Infection with human papillomavirus (HPV) is a major risk factor for anal cancer. Being vaccinated against HPV lowers the risk of anal cancer.
Anal cancer does not commonly spread (metastasize) outside of the pelvis until it is quite advanced. When it does metastasize it generally goes to liver and lungs.