Melanoma of the rectum: a rare entity

Abstract

A 41-year-old man presented with a 6-mo 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 was underwent to an abdomino-perineal resection (APR). 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 one and half years later. Primary anorectal melanoma is a rare and very aggressive disorder. According to current data, one should always perform a S-100 stain when anorectal sarcoma is suspected. A positive S-100 stain suggests the tumour to be most likely a melanoma. Subsequently, thorough dissemination studies need to be performed. Depending on the outcome of the dissemination studies, a surgical resection has to be performed. Nowadays, a sphincter-saving local excision combined with adjuvant loco-regional radiotherapy should be preferred in case of small tumors. The same loco-regional control is achieved with less "loss of function" compared to non-sphincter saving surgery. Only in the case of large and obstructing tumors an abdomino-perineal resection is the treatment of choice.

Figure 1

Histopathological examination of a biopsy taken at rectosigmoidoscopy showed the tumour to be a leiomyosarcoma (HE, × 100).

Figure 2

MRI-rectum showing a tumour just behind the anal verge.

Figure 3

Histopathological examination of the abdomino-perineal resection (S-100 Positive, x 200). S-100 staining performed with an automatic system (Benchmark XT, Ventana Systems). Diffuse expression of S-100 staining typical for melanoma. In leiomyosarcoma, S-100 is never expressed.