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.
Melanoma develops from cells called melanocytes that give skin its colour. Melanoma usually starts in the skin. But there are also small numbers of melanocytes in the mucosa. The mucosa is a tissue that lines various parts of the body including the anus and rectum. Melanoma that develops in the mucosa is called mucosal melanoma.