S-100 staining for the diagnosis of melanoma of the anal canal.

Thirty-two cases of anorectal melanoma are presented. These were diagnosed at the Pathology Department of the All India Institute of Medical Sciences, New Delhi, over a period of 18 years from 1970 to 1988. In 13 cases the clinical diagnosis was carcinoma melanoma was suspected clinically in only 9 of the 32 cases. Epithelioid tumours constituted the majority (26/32) 81%, followed by the pleomorphic type (4/32), 12.5% and then the sarcomatoid variant (2/32) 6.2%. Staining for S-100 protein was done on 21 cases and was found positive in 16/21 or 76%.