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Anal cancer is a rare form of cancer that occurs in the anus. The anus is a 1 1/2-inch tube at the end of your rectum through which stool leaves your body. Muscles called sphincters surround the anus and control bowel movements.

About 4,600 people are diagnosed with anal cancer annually, according to the American Cancer Society. While anal cancer is rare, its incidence appears to be increasing, though it isn't completely clear why.

Treatment for anal cancer in the past typically meant extensive surgery and the removal of the anus. Today doctors have found ways to control anal cancer through radiation and chemotherapy, saving the anus and preserving normal bowel function for anal cancer survivors. But that isn't always possible for late-stage anal cancers. However, the majority of anal cancer is caught in its earliest stages — when treatment provides the best chance for cure.