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 blee ding following bowel movement 2 months previously. Digital and sigmoid oscopic examination of the rectum revealed a 3 x 2 x 1 cm exophytic tu mor with a granular surface in the rectum 35 mm from the dentate line. No increased pigmentation was detected. Biopsy revealed degenerated m ucosa accompanied by severe infiltration of inflammatory cells, but no malignant cells. The tumor and normal mucosa surrounding the tumor wa s excised 12 days after the biopsy. Light microscopy revealed the tumo r to consist of malignant melanocytes and showed that the tumor was su rrounded by normal mucosa. Immunohistochemical staining with antimelan oma antibody and HMB-45 substuntiated the diagnosis. Clinical and labo ratory examination excluded the presence of melanoma at sites other th an rectum. The patient refused an abdomino-perineal resection of the r ectum and combination chemotherapy was performed. She died 18 months a fter the initial operation due to local recurrences and metastases to pelvic lymph nodes, liver, and lung.