Anal cancer is cancer that starts in the anus. Different types of tumors can form in the anus. Some of these tumors are not cancerous and some are cancerous:
Benign or noncancerous anal tumors. Polyps are small growths that may be flat or bumpy or may look like mushrooms. They are not cancer. There are different types of polyps depending on their location and their cause. Inflammatory polyps, lymphoid polyps, and skin tags (also called fibroepithelial polyps) are examples of different kinds of noncancerous polyps. Other types of benign tumors include adnexal tumors, leiomyomas, granular cell tumors, hemangiomas, lipomas, and schwannomas. These are rare.
Anal warts (condylomas). These are growths that usually occur just outside the anus and in the lower anal canal. They are caused by infection with a human papilloma virus. People who have had condylomas are more likely to develop anal cancer.
Precancerous lesions. Many people who develop the most common type of anal cancer first had some patches of irregular cells. Your doctor may call these lesions anal intraepithelial neoplasia (AIN). Each year, a small percentage of of people with AIN develop invasive cancer.
Malignant anal tumors. These are cancerous tumors. The most common type is squamous cell carcinoma. This type of anal cancer begins in the cells that line the anal margin and most of the anal canal. There are other types of malignant anal tumors. Cloacogenic carcinomas (also called transitional cell carcinomas) make up most of the remainder of anal cancers. Adenocarcinomas account for a small number of cases of anal cancer. Other types of malignant anal tumors are very rare.