Original ArticlesPRDM10-rearranged Soft Tissue Tumor A Clinicopathologic Study of 9 CasesPuls, Florian MD, FRCPath*; Pillay, Nischalan MB, ChB, FRCPath, PhD†,‡; Fagman, Henrik MD, PhD*; Palin-Masreliez, Anne BSc*; Amary, Fernanda MD, PhD†; Hansson, Magnus MD, PhD*; Kindblom, Lars-Gunnar MD, PhD*; McCulloch, Tom A. BM, BS, FRCP, FRCPath§; Meligonis, George MBBCh, FCPath(SA)∥; Muc, Ronald MBBCh, FRCPath¶; Rissler, Pehr MD, PhD#; Sumathi, Vaiyapuri P. FRCPath**; Tirabosco, Roberto MD†; Hofvander, Jakob MSc††; Magnusson, Linda MSc††; Nilsson, Jenny MSc††; Flanagan, Adrienne M. MB, BCh, PhD, FRCPath†,‡; Mertens, Fredrik MD, PhD#,††Author Information *Department of Clinical Pathology and Genetics, Sahlgrenska University Hospital, Gothenburg #Department of Clinical Genetics and Pathology, University and Regional Laboratories, Skåne University Hospital, Lund University ††Department of Clinical Genetics, Lund University, Lund, Sweden †Department of Cellular and Molecular Pathology, Royal National Orthopaedic Hospital NHS Trust, Stanmore ‡Research Department of Pathology, University College London Cancer Institute, London §Department of Histopathology, Nottingham City Hospital, Nottingham ∥Department of Histopathology, Addenbrooke’s Hospital, Cambridge ¶Department of Histopathology, Heartlands Hospital, Birmingham **Department of Musculoskeletal Pathology, Royal Orthopaedic Hospital NHS Foundation Trust, Birmingham, UK Conflicts of interest and source of funding: N.P. is funded through a Cancer Research UK Clinician Scientist fellowship. H.F. and F.P. are supported by grants from the Johan Jansson Foundation. F.M. is supported by grants from the Swedish Cancer Society (CAN2017/269) and Region Skåne. A.F. is an NIHR (UK) Senior Investigator. The remaining authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Florian Puls, MD, FRCPath, Department of Clinical Pathology and Genetics, Sahlgrenska University Hospital, Gothenburg 43146, Sweden (e-mail: [email protected]). The American Journal of Surgical Pathology: April 2019 - Volume 43 - Issue 4 - p 504-513 doi: 10.1097/PAS.0000000000001207 Buy SDC Metrics Abstract Gene fusion transcripts containing PRDM10 were recently identified in low-grade undifferentiated pleomorphic sarcomas (UPS). Here, we describe the morphologic and clinical features of 9 such tumors from 5 men and 4 women (age: 20 to 61 y). Three cases had previously been diagnosed as UPS, 3 as superficial CD34-positive fibroblastic tumor (SCD34FT), 2 as pleomorphic liposarcoma, and 1 as pleomorphic hyalinizing angiectatic tumor. The tumors were located in the superficial and deep soft tissues of the thigh/knee region (4 cases), shoulder (2 cases), foot, trunk, and perineum (1 case each) ranging in size from 1 to 6 cm. All showed poorly defined cellular fascicles of pleomorphic cells within a fibrous stroma with frequent myxoid change and a prominent inflammatory infiltrate. All displayed highly pleomorphic nuclear features, but a low mitotic count. Most tumors were well circumscribed. One of 9 tumors recurred locally, but none metastasized. Immunohistochemically, all were CD34+ and showed nuclear positivity for PRDM10; focal positivity for cytokeratins was seen in 5/6 cases. PRDM10 immunoreactivity was evaluated in 50 soft tissue tumors that could mimic PRDM10-rearranged tumors, including 4 cases exhibiting histologic features within the spectrum of SCD34FT. Except for 2/6 pleomorphic liposarcomas and 1/4 myxofibrosarcomas, other tumors did not show nuclear positivity but displayed weak to moderate cytoplasmic immunoreactivity. In conclusion, PRDM10-rearranged soft tissue tumor is characterized by pleomorphic morphology and a low mitotic count. Its morphologic spectrum overlaps with SCD34FT. Clinical features of this small series suggest an indolent behavior, justifying its distinction from UPS and other sarcomas. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.