Primary anorectal melanoma is a rare and very aggressive disorder. A report published on March 14, 2008, in the World Journal of Gastroenterology addresses such a case. A 41-year-old man presented with a 6-month history of changed defecation and rectal bleeding. A 3-cm polypoid tumor of the lower rectum was found at rectosigmoidoscopy, which proved to be a leiomyosarcoma upon biopsy. Dissemination studies did not show any metastases. He underwent an APR. The histopathology of the specimen showed a melanoma (S-100 stain positive). Two years after the resection, metastases in the abdomen and right lung were found. He died a year and a half later.
In the view of the authors, if there is suspicion of an anorectal sarcoma, one should always perform an S-100 stain following a biopsy. A positive S-100 stain indicates that the tumor is most likely to be a melanoma. Depending on the outcome of the dissemination studies, a surgical resection has to be performed. It has been thought that a sphincter-saving local excision combined with adjuvant locoregional radiotherapy should be preferred in the case of small tumors. The same locoregional control is achieved with less loss of function compared to non-sphincter-saving surgery. Only in the case of large and obstructing tumors is an abdominoperineal resection the treatment of choice.
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World Journal of Gastroenterology