Undifferentiated Pleomorphic Sarcoma

Excerpt

The undifferentiated pleomorphic sarcoma (UPS) —formerly known as malignant fibrous histiocytoma, is a high-grade aggressive soft-tissue sarcoma (STS). Mesenchymal stem cells are the most likely origin of the tumor, instead of histiocytes as previously thought. It can affect soft tissues, bones, retroperitoneum, and metastasize to several organs. The earliest reports suggested it was the most common soft-tissue sarcoma (STS) in the adult population. Subsequent analyses employing immunohistochemistry markers and sophisticated cytogenetics demonstrated that many of those tumors corresponded to other types of sarcomas.

Prior subclassifications of MFH into storiform, pleomorphic, myxoid, giant cell, and angiomatoid variants are now rarely utilized. The definition of this tumor has been a matter of debate for more than five decades. Hence, a significant limitation of the historical literature is that only the most recent studies can confidently characterize this entity. At present, UPS is diagnosed by excluding other well-classified STSs.