One aspect of GBM heterogeneity is reflected by the variable transcriptional makeup of the different GBM subtypes, e.g., classical, mesenchymal, and proneural, which are partially enriched for genetic events such as alterations in PDGFRA (proneural subtype) and EGFR (classical) (13, 14). This evidence concerns the gene PDGFRA and glioblastoma.