A Case of Anorectal Malignant Melanoma With Rectal Mucosal Invasion

A case of malignant melanoma of the anorectal region with circumferential mucosal invasion is reported. A 67-year-old male visited our hospital with bloody stools. An I sp-type polyp was found in the anorectal region, 1.5 cm from the dental line, by a colonoscopic examination. Because both the head of the polyp and the circumferential mucosa presented black color, malignant melanoma was suspected, and biopsy was performed from both areas. Pathological examination diagnosed these lesions correctly as malignant melanoma, and the Mile's operation, with lymph node resection (level D2), was performed. The depth of invasion was to the submucosal layer (sm3) in the polyp, and to the mucosal layer (m) in the circumferential mucosa, with no lymph node metastasis. At present, three months after the operation, no findings suggesting recurrence have been observed. Primary malignant melanoma of the anorectal region is a relatively rare entity, and the prognosis is very poor. To improve the prognosis, early diagnosis and the establishment of the standard surgical therapy are necessary.