Rarely, anal cancers develop in glandular tissue (adenocarcinoma). Other uncommon lesions include small cell carcinomas, malignant lymphomas, sarcomas, melanomas or Paget's disease (an intraepithelial adenocarcinoma of the mucous or sweat glands).
The following discussion considers only the common epidermoid cancers.
How It Spreads Anal tumors can extend directly into adjacent tissues, including the skin or sphincter muscle, or into local organs such as the rectum, prostate or vagina. Tumor cells can spread via the lymph system to lymph nodes in the groin or the pelvis. Metastases can also travel through the bloodstream, especially to the liver and lungs.
What Causes It The causes of anal cancer are not known. People who get anal cancer usually have a history of one or more risk factors . It is believed that invasive cancer is preceded by premalignant changes known as intraepithelial neoplasia in the surface linings of the anal canal or anal margin.
