The abnormal growth of cells in the anus is called anal intraepithelial neoplasia (AIN) or anal squamous intraepithelial lesions (SILs). Tumors that develop in or on the anus are either benign (noncancerous) or malignant (cancerous). The different types of anal cancer, listed below, are based on the type of cells in which the cancer develops:
Squamous cell carcinoma begins in the outer lining of the anal canal. It is the most common type of anal cancer.
Cloacogenic carcinoma develops between the outer part of the anus and the lower part of the rectum and accounts for about 25 percent of all anal cancers.
Adenocarcinoma occurs in the mucous-producing glands located beneath the anal lining.
Basal cell carcinoma is a type of skin cancer that may appear in the perianal skin, which is around the anus.
Melanoma begins in pigment-producing cells found in the skin or anal lining.
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