Formation of a Colo-colonic Fistula Communicating with the Transverse Colon in Cecal Cancer: A Case Report.

Although colorectal cancer frequently invades adjacent organs, colon-to-colon invasion is rarely observed, and colo-colonic fistula formation due to colorectal cancer is uncommon. Here we report a case of preoperative diagnosis of cecal cancer that has invaded the transverse colon. A 69-year-old woman presented with diarrhea and a palpable mass in the lower right abdomen. After being diagnosed with double cancer involving the cecum and transverse colon at a previous hospital, she was referred to our hospital. CT scans revealed enhanced mass-like wall thickening in both the cecum and transverse colon, with 3D-CT suggesting a cecal tumor invading the transverse colon. The accurate preoperative diagnosis and prediction of fistula formation led us to perform curative resection using laparoscopic surgery. The resected specimen contained an ulcerated moderately differentiated adenocarcinoma measuring 6.0 cm × 4.5 cm in the cecum. Additionally, a fistula originating from the cecal cancer and communicating with the transverse colon was identified. The tumor was classified as stage IIIC (T4b, N1, M0). When multiple masses are identified in the colon, it is important to consider the possibility of the primary tumor invading neighboring organs and the potential for fistula formation.