Malignant melanoma of the anus: report of 12 patients and analysis of 255 additional cases.

The authors present a report of 12 patients with anal melanoma (AM) and review 255 cases reported since 1947. Combining these patients with those from the literature, the authors analyze several aspects of AM that are controversial or have not been studied in a systematic manner. The mean clinical tumor size was 4.1 cm. Seventy per cent were grossly pigmented, 63 per cent were polypoid, and 44 per cent were prolapsed. Two-thirds of AM were located in the proximal pecten, at or near the level of the anal valves. Microscopically, the most useful diagnostic criteria were melanin production, junctional change, and a nesting growth pattern. In four of the authors' cases, atypical junctional change extended laterally from the overt invasive neoplasm for distances up to 1 cm. Approximately 60 per cent of patients had metastases at the time of diagnosis. There was no statistical difference in determinate survivals of patients treated for cure by local excision and abdominoperineal resection. Neither tumor size nor configuration affected survival. The choice of therapy was not influenced by tumor size.