Adapted for the Canadian edition by Bernard Cummings, MB, ChB
Cancer of the anus—the 2.5 cm (1 in.) tube where the rectum opens onto the body surface—is less common than other bowel cancers, accounting for only about 1 to 2 percent of all cancers of the large bowel and its outlet. Fewer than 1,000 cases occur annually in Canada.
Anal cancer is highly treatable and often curable, especially in the early stages. The first sign of the cancer is often bleeding, which may be mistaken for hemorrhoids or other benign anal disease. Many cancers first appear as an ulcer . Anal cancers are sometimes discovered by a pathologist in a specimen from a surgical operation done for apparently benign disease.
Types The vast majority—80 to 90 percent—of all primary cancers of the anus develop in the skin-like lining of the anal canal or in the skin immediately adjacent to the anal opening. These skin-like (epidermoid) cancers include squamous cell carcinomas and less common sub-types such as basaloid and transitional cell carcinomas. A rare variant is mucoepidermoid cancer. Squamous cell cancers may arise in the skin around the anus (anal margin or perianal area). Bowen's disease is a premalignant in situ squamous cell lesion of the skin around the anus.
