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BCOR immunohistochemistry, but not SATB2 immunohistochemistry, is a sensitive and specific diagnostic biomarker for central nervous system tumours with BCOR internal tandem duplication

Central nervous system (CNS) tumors with the BCOR (BCL6 Corepressor) internal tandem duplication (ITD) were recently isolated by a DNA-methylation profile from a series of primitive neuroectodermal tumors [1]. They are mainly characterized by a recurrent BCOR ITD and express BCOR by immunohistochemistry (IHC) [2]. In rare cases, they present an EP300-BCOR fusion inducing the absence of expression of BCOR by IHC [3]. In soft tissue and kidney tumors with different types of BCOR alterations, SATB2 has been considered a diagnostic hallmark and BCOR IHC is not highly specific in some other contexts (soft tissue and uterine tumors) [4]. In a recent paper, SATB2 immunoexpression has been evidenced in one CNS-tumor with proven BCOR ITD [5]. The aim of our study was to evaluate the sensitivity and specificity of the BCOR and SATB2 immunostainings in a large cohort of pediatric CNS tumors.