Primary anorectal malignant melanoma: clinical features and results of surgical therapy in Singapore--a case series.

INTRODUCTION Primary malignant melanoma arising from the anorectum is uncommon. The natural history of anorectal malignant melanoma is that of a very poor prognosis with early dissemination of disease. Successful surgical treatment has been rare. The present series reviews the clinical features and results of surgical management of patients with anorectal malignant melanoma treated in the Department of Colorectal Surgery, Singapore General Hospital. MATERIALS AND METHODS Data for all patients treated for anorectal malignant melanoma during an 11-year period from 1989 to 1999 were reviewed. The age, sex, presenting symptoms, duration of symptoms prior to diagnosis, size of tumour, extent of disease, type of surgery and length of survival were analysed. RESULTS Four men and 2 women, ranging in age from 31 to 81 years with histologically proven primary anorectal malignant melanoma, were included in the study. The most common (67%) presenting symptom was rectal bleeding. The mean tumour size was 2.5 cm (range 1 to 5 cm). All underwent abdomino-perineal resection. Three died of disseminated disease within 17 months while the other 3 were still alive at the time of this study; the longest up to 6.5 years from the time of diagnosis. CONCLUSION The prognosis of primary anorectal malignant melanoma is poor. However, it is worthwhile treating aggressively as long-term survivor may be encountered in some.