[Primary melanoma of the rectum: an infrequent neoplasia with an atypical presentation].

Primary anorectal melanoma is a rare malignancy with an extremely aggressive biological behaviour. The main clinical presentations are local symptoms such as rectal bleeding, anal mass or pain, or a change in bowel habits. The tumour is frequently mistaken for benign conditions as haemorrhoids or rectal polyps. Many treatments can be used: surgery, chemotherapy, radiotherapy, immunotherapy and even bio-therapy. Despite this, the disease has a very poor prognosis and 10% of patients survive 5 years.