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 (shown here), 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 shows an example of inflammatory subtype of UPS. The neoplastic cells (with atypical hyperchromatic nuclei) are present in a background of neutrophilic and xanthomatous infiltrate. These cases can mimic and be mistaken for lymphomas. Magnification: x200.