Clinicopathological and molecular characteristics of round cell sarcoma with EWSR1::PATZ1 fusions

HUANG Linlin; XU Zhiyu; LIANG Chuntao; LIU Hengjing; WANG Ling

doi:10.3969/j.issn.1007-8096.2025.11.1490

Abstract：Objective To investigated the clinicopathological,immunophenotypes,molecular features and differential diagnosis of round cell sarcoma with EWSR1::PATZ1 fusions(EWSR1-non-ETS fusions).Methods We retrospectively analysed the clinical data,pathomorphology,immunophenotype and molecular of one EWSR1::PATZ1 sarcomas case diagnosed at the Department of Pathology,KingMed Diagnostics in 2023.The related literature was also reviewed.Results The patient was an 11-year-old boy with a solid mass of approximately 3.0 cm×1.5 cm×1.0 cm in the left parietal-occipital region of the skull.Microscopically,the tumor was diffuse oval or short spindle cell with solid papillary patterns.The tumor cells had abundant eosinophilic or clear cytoplasm,irregular nuclear membranes,frequent mitoses,focal necrosis,and hyaline degeneration of the interstitial blood vessels.Immunohistochemically,the tumor cells showed weakly positive for CD99,negative for DES,CgA,GFAP,PCK,S-100,ERG,with high Ki67 index reaching 60%.Fluorescence in situ hybridization(FISH)identified EWSR1 gene rearrangement.Next-generation sequencing(NGS)detected EWSR1::PATZ1 fusions and TP53 p.Y103* inactivation mutation.The patient was treated with CAV/IE chemotherapy regimen after surgery and was followed up for 19 months without disease recurrence.Conclusion Round cell sarcoma with EWSR1::PATZ1 fusions is a newly named rare sarcoma with a wide range of age,diverse morphology and immunophenotype.It needs to be differentiated from a variety of tumors.Detection of the EWSR1::PATZ1 fusion is the gold standard for diagnosis.There is no standard treatment and the prognosis is relatively poor.