What is anal cancer? Cancer cells that form into benign or malignant tumors in the tissues of the anus are anal cancer. The anus is the opening at the bottom of your intestines where stools exit the body. Some noncancerous forms of anal cancer can turn cancerous over time. Anal cancer is rare and may spread to other parts of the body. Types of anal cancer There are various forms of anal cancer, each defined by the type of tumor that develops. A tumor is an abnormal growth in the body. Tumors can either be benign or malignant. Malignant tumors can and will spread to other parts of the body over time. Examples include: Benign tumors: These include noncancerous tumors in the anus, such as polyps, skin tags, granular cell tumors, and condylomas (genital warts). Precancerous conditions: This refers to benign tumors that may become malignant over time, which are common in anal intraepithelial neoplasia (AIN) and anal squamous intraepithelial neoplasia (ASIL). Squamous cell carcinoma: This is the most common type of anal cancer in the United States, according to the American Cancer Society. These malignant tumors in the anus are caused by squamous cells (cells that line most of the anal canal). Bowen’s disease: Also known as squamous cell carcinoma in situ, this condition is characterized by abnormal cells on anal surface tissue that haven’t invaded deeper layers. Basal cell carcinomas: This type of skin cancer affects skin exposed to the sun. It’s a very rare form of anal cancer. Adenocarcinoma: This is a rare form of cancer that arises from the glands surrounding the anus. Gastrointestinal stromal tumors: These cancers can form anywhere in the gastrointestinal (GI) tract, but they most commonly occur in the small intestines and stomach.
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