Primary malignant melanoma of the rectum.

We present a case of primary malignant melanoma arising in the rectum of a 71-year-old woman who had presented with intermittent rectal bleeding following bowel movement 2 months previously. Digital and sigmoidoscopic examination of the rectum revealed a 3 x 2 x 1 cm exophytic tumor with a granular surface in the rectum 35 mm from the dentate line. No increased pigmentation was detected. Biopsy revealed degenerated mucosa accompanied by severe infiltration of inflammatory cells, but no malignant cells. The tumor and normal mucosa surrounding the tumor was excised 12 days after the biopsy. Light microscopy revealed the tumor to consist of malignant melanocytes and showed that the tumor was surrounded by normal mucosa. Immunohistochemical staining with antimelanoma antibody and HMB-45 substuntiated the diagnosis. Clinical and laboratory examination excluded the presence of melanoma at sites other than rectum. The patient refused an abdomino-perineal resection of the rectum and combination chemotherapy was performed. She died 18 months after the initial operation due to local recurrences and metastases to pelvic lymph nodes, liver, and lung.