Abstract
An undifferentiated pleomorphic sarcoma (UPS), also known as a malignant fibrous histiocytoma in the past, commonly involves the soft tissue of the extremities and the retroperitoneum. However, a primary UPS of the colon mesentery is very rare. A 69-year-old male patient visited our outpatient department for treatment of an enlarged, palpable mass in the right lower quadrant (RLQ). Computed tomography showed a 15-cm multilobulated, heterogeneous, enhanced mass in the RLQ, which we suspected originated from the colon. He underwent a right hemicolectomy, and the pathologic result was a colon mesenteric UPS. We report a rare case of a primary UPS of the colon mesentery and discuss the characteristics of this neoplasm in reference to the literature.