IDH1 and glioblastoma: Based on the expression of 840 genes, the researchers classified GBM into four distinct subtypes: classical (EGFR amplification and CDKN2A deletion), mesenchymal (NF1 deletion and expression of mesenchymal markers), proneural (PDGFRA amplification, IDH1 mutation and expression of proneural development genes), and neural (expression of neuronal markers)8.