To simplify, we may say that classical GBM is characterized by EGFR amplification; deletion of the CDKN2A locus; and overexpression of the NES (a neural precursor and stem cell marker), Notch (NOTCH3, JAG1, and LFNG), and Sonic hedgehog (SMO, GAS1, and GLI2) signaling pathways. Here, EGFR is linked to glioblastoma.