Anorectal melanoma comprises about one percent of all anorectal carcinomas. Typically presenting in the age range of 50-60 and predominantly in women, this type of cancer has a fairly low survival rate. Melanoma is the deadliest form of skin cancer, and metastases pose a fatal risk in this disease. Melanoma starts in skin cells called melanocytes, which provide pigment to the skin. Melanocytes are also found in the lining of the anus and rectum, and these cells can grow out of control and form malignant tumours. For these reasons, a change in the colour, size or shape of a mole is usually the first sign of melanoma.
Symptoms associated with anorectal melanoma can include bleeding from the anus, pain, itching, a lump in the area, or a change in bowel habits (diarrhea, constipation, or incontinence).
The diagnosis will begin with an external examination of the anorectal area, followed by a biopsy if a lesion is discovered. The doctor will also examine the groin area for swollen lymph nodes. Other tests that can be administered are full-body CT scans to see if the tumour has spread beyond the anal region, magnetic resonance imaging (MRI) scans to see a more detailed picture of the suspected cancerous region, or ultrasound of the rectum and the groin to detect tumour changes and to easily obtain a biopsy.
The treatment for this type of cancer is surgery; however, there is no consensus on the preferred type of surgical procedure. The choices range from an abdomino-perineal resection (removal of the anus and the rectum) to local excision of the tumour with or without concurrent (adjuvant) radiotherapy. When the tumour cannot be completely removed by a local excision, and involves structures in the anus or rectum that may cause a loss of bowel control (incontinence), an abdomino-perineal resection might be chosen. In this case, a stoma (opening) is placed on the abdominal wall and a bag is attached to it to allow for bowel function and excretion.
Radiotherapy involves exposure to intense rays that kill the any tumour cells left over after surgery. This radiation will be applied to the anal region, the lymph nodes, and to any other areas where the tumour might have spread. Chemotherapy will be used only when other treatments are not possible or if the cancer returns.