A Case of Sigmoid Colon Cancer with a Large Synchronous Anal Metastasis

Abstract

A 73-year-old man was rushed to the hospital because of bleeding from an anal mass. A large necrotic tumor, 13 cm in diameter, was present in the perianal region, on the right side. Biopsy of the anal tumor revealed moderately differentiated adenocarcinoma. Subsequent colonoscopy showed sigmoid colon cancer, and the histopathological findings were similar to those of the anal tumor. Abdominal CT revealed wall thickening of the sigmoid colon, and metastasis to the regional lymph nodes and multiple para-aortic lymph nodes, besides the perianal mass. FDG-PET revealed elevated uptake in the sigmoid colon, para-aortic lymph nodes and the perianal tumor. Based on the findings, the patient was diagnosed as having sigmoid colon cancer with a synchronous anal metastasis. Abdominoperineal rectal resection with extended perineal resection was performed. Pelvic floor reconstruction was performed using a vertical rectus abdominis musculocutaneous flap and a gluteal fold flap. Histopathological examination showed moderately differentiated adenocarcinoma. The perianal tumor showed similar histological findings. Because the sigmoid colon cancer showed high lymphatic invasion, and high venous invasion, the anal metastasis was thought to have occurred via the lymphovascular route. Subsequently, the patient received systemic chemotherapy, and has shown no evidence of progression for 12 months since the surgery. We report a rare case of sigmoid colon cancer with a synchronous anal metastasis, with a review of the literature.