[Primary ano-rectal melanoma. Report of 9 cases]

We report nine cases of anorectal melanoma illustrating the histopathological features of these tumors. In all cases, the diagnosis was made at symptomatic stage. Eight patients were treated by surgical procedure which consisted of abdominal perineal resection or local excision. The tumor was either monomorphous, composed of epithelioid or spindle cells, or polymorphous containing both cell types. One case was characterized by small cells resembling plasma cells. Pigmentation was inconstant. Tumor cells were marked by antibodies directed against the S100 protein (9 cases/9), HMB45 (4 cases/7) and vimentin (5 cases/7). As suggested by these cases, the diagnosis of melanoma should be systematically kept in mind in case of an anorectal tumor with unusual histopathological features.