Anorectal melanoma is a rare cancer that starts in the anus or rectum (back passage), or both. The anus and rectum are parts of the digestive system. The rectum is the last section of the large bowel. The anus is the ring of muscle below the rectum. It controls when bowel motions leave your body.
Although melanoma is a cancer that usually starts in the skin, it can occasionally develop in other parts of the body. Melanoma develops from cells called melanocytes that give our skin its colour. Melanoma usually develops in the skin. But because there are melanocytes in different parts of the body, it can occasionally start in other areas, such as the lining of the anus or rectum.