Central nervous system high grade neuroepithelial tumor with BCOR immunopositivity: Is there a molecular heterogeneity?

Central nervous system high grade neuroepithelial tumor - BCOR altered is a newly defined entity which is characterised by internal tandem duplication (ITD) in exon 15 of BCOR. These tumors resemble high grade glioma histologically and exhibit BCOR immunopositivity. However, recently fusions of BCOR are also described in CNS lower grade gliomas, thus questioning the sensitivity and specificity of BCOR immunohistochemistry for identification of BCOR-ITD. We describe four cases of high grade neuroepithelial tumor with BCOR immunopositivity which were diagnosed over a period of one year at our institute. Amongst these, only one tumor revealed BCOR-ITD on sequencing. SATB2 immunopositivity which is a sensitive marker of BCOR-ITD, BCOR fusions and YWHAE fusions was noted in three out of four cases. Our study suggests that BCOR immunopositive CNS high grade tumors are molecularly heterogeneous and could harbour genetic alterations other than BCOR-ITD.