U Undifferentiated Pleomorphic Sarcoma Alessandro Franchi Department of Translational Research and of New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy Synonyms Malignant fibrous histiocytoma Definition Undifferentiated pleomorphic sarcoma (UPS) is a malignant mesenchymal tumor with no identifi- able line of differentiation. It is a therefore diag- nosis of exclusion. Clinical Features • Incidence UPS originating in the genitourinary tract is rare, and literature consists mainly of single case reports. • Age UPS is a tumor of adults, arising mainly in patients between the fifth and the eight decades. • Sex It occurs predominantly in males. • Site Genitourinary UPS arises more frequently in the urinary bladder, but few examples have also been reported in the kidney, the prostate, and the spermatic cord (Kunze et al. 1994; Kulmala et al. 1994; Ptochos et al. 1999; Demir et al. 2012). • Treatment Treatment is surgical, combined in some cases with chemotherapy and radiation. • Outcome UPS is an aggressive tumor with frequent local and distant relapse and a poor prognosis. Macroscopy UPS usually appears as a large multilobulated gray-white, fleshy mass. The cut surface often shows hemorrhagic, myxoid, and/or necrotic changes. Microscopy The tumor is composed by an admixture of spin- dle and pleomorphic cells, set in a variably collagenized, sometimes focally myxoid, extra- cellular matrix (Fig. 1). Tumor cells are organized in fascicular and cartwheel (storiform) patterns. © Springer Nature Switzerland AG 2020 M. R. Raspollini, A. Lopez-Beltran (eds.), Uropathology , Encyclopedia of Pathology, https://doi.org/10.1007/978-3-030-41894-6