Strong OLIG2 expression in supratentorial ependymoma, ZFTA fusion‐positive: A potential diagnostic pitfall

Abstract

Ependymomas (EPN) are central nervous system neoplasms that exhibit an ependymal phenotype. In particular, supratentorial EPN (ST‐EPN) must be differentiated from more aggressive entities such as glioblastoma, IDH‐wildtype. This task is frequently addressed with the use of immunohistochemistry coupled with clinical presentation and morphological features. Here we describe the case of a young adult presenting with migraine‐like symptoms and a temporoinsular‐based expansile mass that was first diagnosed as a GBM, mostly based on strong and diffuse oligodendrocyte transcription factor 2 (OLIG2) expression. Molecular characterization revealed a ZFTA::RELA fusion, supporting the diagnosis of ST‐EPN, ZFTA fusion‐positive. OLIG2 expression is rarely reported in tumors other than GBM and oligodendrocyte‐lineage committed neoplasms. The patient was treated with radiotherapy and temozolomide after surgery and was alive and well at follow‐up. This report illustrates the need to assess immunostains within a broader clinical, morphological and molecular context to avoid premature exclusion of important differential diagnoses.