Epithelioid glioblastoma with microglia features: Potential for novel therapy

Epithelioid glioblastoma (E-GBM) was recently designated as a subtype of glioblastoma (GBM) by the World Health Organization (2016). E-GBM is an aggressive and rare variant of GBM that primarily occurs in children and young adults. Although most characterized cases of E-GBM harbor a mutation of the BRAF gene in which valine (V) is substituted by glutamic acid (E) at amino acid 600 (BRAF-V600E), in addition to telomerase reverse transcriptase promoter mutations and homozygous CDKN2A/B deletions, the origins and cellular nature of E-GBM remain uncertain. Here we present a case of E-GBM that exhibits antigenic and functional traits suggestive of microglia. Although no epithelial (e.g., CKAE1/3, epithelial membrane antigen [EMA]) or glial (e.g., GFAP, Olig2) markers were detected by immunohistochemical staining, the microglial markers CD68 and Iba1 were readily apparent. Furthermore, isolated E-GBM-derived tumor cells expressed microglial/macrophage-related genes including cytokines, chemokines, MHC class II antigens, lysozyme, and the critical functional receptor, CSF-1R. Isolated E-GBM-derived tumor cells were also capable of phagocytosis and cytokine production. Treating E-GBM-derived tumor cells with the BRAF-V600E inhibitor, PLX4032 (vemurafenib), resulted in a dose-dependent reduction in cell viability that was amplified by addition of the CSF-1R inhibitor, BLZ945. The present case provides insight into the cellular nature of E-GBM and introduces several possibilities for effective targeted therapy for these patients.

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S7725 BLZ945 BLZ945 is an orally active, potent and selective CSF-1R inhibitor with IC50 of 1 nM, >1000-fold selective against its closest receptor tyrosine kinase homologs. (19) (3)

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