PIK3CA and glioblastoma: Whether these changes affect the expression patterns of hallmark genes in GBM between tissues and derived cultures, was assessed by comparing expression levels of the hallmark genes EGFR, PDGFRA, PTEN, CDK4, RB1, TP53, MET, MYC, HIF1A, PIK3CA, STAT3 as well as MGMT (Fig. 1e).