PLAG1 gene fusions were recently identified in a subset of uterine myxoid leiomyosarcomas (M-LMS). However, we have encountered cases of PLAG1-rearranged uterine sarcomas lacking M-LMS-like morphology and/or any expression of smooth muscle markers. To better characterize their clinicopathologic features, we performed a multiinstitutional search that yielded 11 cases. The patients ranged in age from 34 to 72 years (mean, 57 years). All tumors arose in the uterine corpus, ranging in size from 6.5 to 32 cm (mean, 15 cm). The most common stage at presentation was pT1b (n = 6), and 3 cases had stage pT1 (unspecified), and 1 case each presented in stages pT2a and pT3b. Most were treated only with hysterectomy and adnexectomy. The follow-up (range, 7-71 months; median, 39 months) was available for 7 patients. Three cases (7-21 months of follow-up) had no evidence of disease. Three of the 4 remaining patients died of disease within 55 to 71 months, while peritoneal spread developed in the last patient, and the patient was transferred for palliative care at 39 months. Morphologically, the tumors showed a high intertumoral and intratumoral heterogeneity. M-LMS-like and epithelioid leiomyosarcoma-like morphology were present in 3 and 5 primary tumors, respectively, the remaining mostly presented as nondescript ovoid or spindle cell sarcomas. Unusual morphologic findings included prominently hyalinized stroma (n = 3), adipocytic differentiation with areas mimicking myxoid liposarcoma (n = 2), osteosarcomatous differentiation (n = 1), and undifferentiated pleomorphic sarcoma-like areas (n = 1). The mitotic activity ranged from 3 to 24 mitoses per 10 high-power fields (mean, 9); 3 of 10 cases showed necrosis. In 3 of 11 cases, no expression of smooth muscle actin, h-caldesmon, or desmin was noted, whereas 5 of 5 cases expressed PLAG1. By RNA sequencing, the following fusion partners were identified: PUM1, CHCHD7 (each n = 2), C15orf29, CD44, MYOCD, FRMD6, PTK2, and TRPS1 (each n = 1). One case only showed PLAG1 gene break by fluorescence in situ hybridization. Our study documents a much broader morphologic spectrum of PLAG1-rearranged uterine sarcomas than previously reported, encompassing but not limited to M-LMS-like morphology with occasional heterologous (particularly adipocytic) differentiation. As it is currently difficult to precisely define their line of differentiation, for the time being, we suggest using a descriptive name "PLAG1-rearranged uterine sarcoma."

Bioptical Laboratory Ltd Pilsen Czech Republic

Bioptical Laboratory Ltd Pilsen Czech Republic; Department of Pathology Charles University Faculty of Medicine in Pilsen Pilsen Czech Republic

Department of BioPathology Anticancer Center Institut Bergonié Bordeaux France

Department of Gynecology and Obstetrics Charles University Faculty of Medicine in Pilsen and Charles University Hospital Pilsen Pilsen Czech Republic

Department of Laboratory Medicine and Pathology Mayo Clinic Jacksonville Florida

Department of Laboratory Medicine and Pathology Mayo Clinic Rochester Minnesota

Department of Oncology and Radiotherapeutics Charles University Faculty of Medicine in Pilsen Pilsen Czech Republic

Department of Pathology and Laboratory Medicine Zucker School of Medicine at Hofstra Northwell Hempstead New York

Department of Pathology The Johns Hopkins Medical Institutions Baltimore Maryland

Institute of Pathology Friedrich Alexander University Erlangen Nürnberg University Hospital Erlangen Germany

Institute of Pathology University Hospital Heidelberg Heidelberg Germany

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