Undifferentiated Pleomorphic Sarcoma

Undifferentiated Pleomorphic Sarcoma (UPS) of the Kidney: Microscopically, UPS shows diverse morphologic patterns 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. Most cases have an admixture of storiform and pleomorphic areas with the latter dominating the picture. The storiform pattern (shown here) resembles dermatofibrosarcoma protuberans but is less pronounced. It consists of short fascicles of plump spindle cells arranged in a storiform pattern around blood vessels. Atypical cells with one or more irregular, hyperchromatic nuclei are admixed with spindle cells. Mitotic activity is increased with typical and atypical mitoses. Chronic inflammatory cells, including lipid-laden macrophages (xanthoma cells) are frequently present.