FLT3 and glioblastoma: High levels of ligands for these regulators, CSF-1 and SCF, have been found in patient-derived glioma cell lines.11,12 Microglia depletion in orthotopic GBM models through inhibition of CSF-1 has been shown to decrease spread and tumor burden.12,13 Pexidartinib (PLX3397) is an oral, selective small-molecule inhibitor of CSF1R, KIT, and oncogenic FLT3 (the receptor for FLT3 ligand), making it an ideal candidate for a therapeutic approach aimed at altering the TME.