A Case of Unclassified/Undifferentiated Sarcoma of the Rectum

Abstract

A 57-year-old woman was referred to the hospital due to hematochezia. Colonoscopy showed a 50-mm tumor at the rectum above the peritoneal reflection. Computed tomography and magnetic resonance imaging also showed the tumor at the posterior wall of the rectum. It was diagnosed as a poorly differentiated adenocarcinoma, after which laparoscopic low anterior resection was performed. The tumor appeared to arise from the mucosal epithelium, and histopathological examination showed necrotic tissue and pleomorphic atypical cells. On immunostaining, only vimentin and Ki-67 were positive, but epithelial markers and surface markers of blood cells were negative. In this case, only a mesenchymal marker was positive, and the tumor cells resembled undifferentiated pleomorphic sarcoma. However, undifferentiated pleomorphic sarcoma is a soft tissue tumor, and it has never been previously reported that undifferentiated pleomorphic sarcoma of the colon or rectum arose from mucosal epithelium. Therefore, the diagnosis was undifferentiated pleomorphic sarcoma in undifferentiated/unclassified sarcoma arising from mucosal epithelium. The patient is alive 2 years and 4 months later without recurrence or metastasis.