Primary Mesenteric Undifferentiated Pleomorphic Sarcoma

Undifferentiated pleomorphic sarcoma (UPS), previously known as malignant fibrous histiocytoma, is the most common sarcoma appearing in late adult life. By definition, although the malignant cells tend to appear fibroblastic or myofibroblastic, they should not show differentiation towards a more specific line of differentiation. In this sense, as the pathological and molecular diagnostic techniques have improved in the last few years, in many cases previously classified as malignant fibrous histiocytoma, a more specific diagnosis can be confidently made. In those remaining true cases of UPS, the most frequent localization is the extremities, followed by the retroperitoneum. On the other hand, visceral and intra-abdominal primary involvement is rare.