Synchronous Primary Anorectal Melanoma and Sigmoid Adenocarcinoma: A Case Report

Synchronous primary anorectal melanoma and colorectal adenocarcinoma is extremely rare, with only 5 cases reported in the literature. Here, a case is reported and the currently available literature is summarized. A 72-year-old white male presented with changes in his bowel habits and unintentional weight loss. Colonoscopy revealed a polypoid mass in the distal rectum extending to the anal verge anteriorly and a circumferential polypoid mass in the distal sigmoid colon. Biopsies were taken, which revealed poorly differentiated melanoma of the anorectal mass and moderately differentiated adenocarcinoma of the sigmoid mass with nodal involvement. Computed tomography of the abdomen showed liver metastasis. An extended abdominoperineal resection was undertaken for palliation, relief of symptoms, and definitive histology to guide further management. Consequently, a resection of the hepatic metastasis was attempted; however, macroscopic deposits were discovered on 7 of 8 liver segments perioperatively. He was subsequently referred to medical oncology for palliative chemotherapy. Synchronous primary anorectal melanoma and colorectal adenocarcinoma is rare, this being the sixth report found in the literature. In summary of the available cases, all synchronous cancers were located in the rectosigmoid and had very similar presentations. Most presented relatively late and were generally treated with abdominoperineal resection, which appears to be the best treatment option. Overall, prognosis appears to be dismal. General and colorectal surgeons should always be aware of the possibilities of simultaneous primary cancers because this can affect treatment modalities and prognosis for the patient.