Glioneuronal tumors PATZ1-fused: clinico-molecular and DNA methylation signatures for a variety of morphological and radiological profiles.

The neuroepithelial tumor, PATZ1-fused (NET-PATZ1), has been recently isolated as a distinct methylation class by DNA-methylation profiling and is characterized by recurrent PATZ1 fusions, in association with the EWSR1 or MN1 genes and a chromosome 22 chromothripsis. The clinical phenotype is mainly pediatric and features circumscribed supratentorial tumors. However, the histopathology is vastly heterogeneous (glial, glioneuronal, sarcomatous, multiphenotypic) and a cell of origin has not yet been identified, explaining the previsionary imprecise terminology of "NET". Moreover, extra-central nervous system (CNS) sarcomas also harboring the EWSR1::PATZ1 fusion have been reported and added to the current World Health Organization (WHO) Classification of Soft Tissue and Bone Tumors, in the chapter on undifferentiated small round cell sarcomas. However, their relationship to their CNS counterparts has not yet been studied. Herein, we analyzed a cohort of twelve CNS tumors with PATZ1 fusions in terms of clinical presentation, radiology, histopathology, immunohistochemistry, ultrastructure and DNA-methylation profiling and compared them to five extra-CNS sarcomas-PATZ1. Based on the reported GATA2 overexpression in NET-PATZ1, we also studied the potential interest of GATA2 immunoexpression as a diagnostic tool. We confirmed their distinct molecular characteristics and clinical phenotype but evidenced a morphological intratumoral heterogeneity with three recurrent morphological patterns (oligodendroglial-like, pleomorphic xanthoastrocytoma-like and spindle cells). Despite the unusual spindle and proliferative component in a CD34 + glioneuronal tumor (using electronic microscopy), these tumors present a favorable prognosis. Their histopathological features were all clearly distinct from their soft tissue counterparts. GATA2 immunostaining is highly specific for CNS tumors PATZ1-fused, but its sensitivity is perfectible and further studies are needed to confirm its use as a diagnostic tool. To conclude, our work highlights that CNS tumors, PATZ1-fused seem to represent a novel pediatric glioneuronal tumor type exhibiting a polymorphous morphology and provides new support for its addition as a provisional emerging pediatric circumscribed glioneuronal tumor type, low grade.