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), inflammatory, and giant cell type (shown here). 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 shows giant cell type of UPS (previously referred to as giant cell MFH or malignant giant cell tumour of soft parts). Such cases have an admixture of spindled, rounded, and osteoclast-type giant cells, several of which are seen in this field. Magnification: x400.