Anorectal melanoma: report of two cases.

We have described the clinicopathologic findings in two cases of anorectal melanoma, and extracted the salient features from the medical literature. The disease is rare. Melanoma arises from the anal squamous membrane and very often spreads upward through submucosal planes, producing secondary satelites in the rectum. Trauma from defecation, vast lymphatic and venous systems in the anorectal region, and high invasiveness of the tumor cells eviden;ly account for early distant metastases. Histologically, the neoplastic cells often mimic other cancers. Treatment is surgical, with dismal end results.