Undifferentiated pleomorphic sarcoma, light micrograph. Undifferentiated pleomorphic sarcoma (UPS) is a high-grade sarcoma arising in deep soft tissues in elderly patients. It was previously known as malignant fibrous histiocytoma (MFH) and included a wide range of high-grade pleomorphic sarcomas with varied histogenesis. UPS has a broad spectrum of morphologic appearances and it can be divided into four subtypes: storiform-pleomorphic (prototypic UPS, 70% of cases), myxoid (myxofibrosarcoma, 20% of cases; shown here), inflammatory, and giant cell type. Most cases show an admixture of pleomorphic and storiform areas with sheets of polygonal, spindled and epithelioid cells, abundant eosinophilic cytoplasm, marked nuclear pleomorphism, multinucleation, necrosis and conspicuous mitotic activity, including atypical forms. This image is an example of myxofibrosarcoma (previously referred to as myxoid MFH) and consists of spindle and atypical giant or multinucleated cells in a background of myxoid stroma. Magnification: x200.