[Rectal Mucinous Cancer with Submucosal Tumor-Like Morphology Preoperatively Diagnosed Using EUS-FNAB - A Case Report].

A man in his 70s presented with a chiefcomplaint ofbleeding during bowel movements. Subsequent colonoscopy revealed a submucosal tumor-like elevated lesion ofapproximately 4 cm situated in the sigmoid section ofthe rectum. EUS-FNAB was performed, and the lesion was identified as mucinous cancer. Based on a diagnosis of rectal cancer(cT4a, cN0, cM0, cStage II), a low anterior resection was performed. Histopathological analysis of the resected specimen revealed a well-differentiated mucinous cancer. The tumor had ruptured the proper muscular layer and was developing in a submucosal tumor-like manner, protruding from the wall within a fibrous capsule. In Japan, only 15 cases of submucosal tumor-like colorectal mucinous cancer have been reported to date. It is rare for such cases to be preoperatively diagnosed as mucinous cancer using EUS-FNAB and then to undergo radical resection.