Malignant melanoma of the anorectum--a rare entity

Primary anorectal melanoma is a rare entity with a poor prognosis accounting for approximately 0.1-4.6% of anal tumours and 0.5-1.6% of all melanomas. Almost 60% of patients have already disseminated disease at initial diagnosis.

We report four cases of anorectal melanoma treated at our department from November 2006 to September 2008, as well as a review of the literature.

There were two females and two males, of median age 69 years (range: 59-81 years). Most frequent complaints were rectal bleeding and/or anorectal pain. Three of our four patients had amelanotic melanomas. We found the positive expression of S-100 protein and HMB-45 in two patients and melanin A cells in one case. Abdominoperineal resection was performed in two patients, colostomy in one patient and a wide local excision also in one case. Three patients died on account of dissemination of melanoma, one patient is still alive.

Anal melanoma remains a deadly problem. Clear guidelines for the therapy of anorectal melanoma have not been established. This mainly results from the rarity of this tumour. Treatment is based on retrospective studies, which report a limited number of cases.