[Cancer of the anus: incidence and behavior of melanoma in our series].

From January 78, to December 88, we have treated 717 cases of colorectal carcinoma; 136 were located less than 5 cm from the anal margin. There were 117 adenocarcinomas; it was difficult to decide if the origin was the anal canal or the rectal ampulla. The remaining 19 tumors were: 9 malignant melanomas, 6 squamous cell carcinomas, 3 cloacogenic carcinomas, 1 rectal carcinoid, 1 leiomyosarcoma. We point out the high incidence of anal melanoma, 47.36% of total number of anal cancers, excluding adenocarcinomas. The clinical diagnosis was cancer of the anus; melanoma was not suspected in any of the cases. In 5 cases the preoperative biopsy did not diagnose melanoma. Since lesions were considered resectable, surgical treatment was always abdominoperineal resection. Pathological study of the surgical specimen showed lymph node metastases in all cases, in contrast to only 45.87% of adenocarcinomas. When lymph nodes were infiltrated by the tumor there were no differences in survival of patients with malignant melanoma and adenocarcinoma; nevertheless, when comparing the total group of patients with adenocarcinoma there were important differences. Summarizing, the diagnosis of malignant melanoma of the anus, compared to adenocarcinoma, implies a poor prognosis, probably related to the highest tendency to spread to the lymph nodes.