EGFR and glioblastoma: Studies have shown that STAT3 is upregulated in GBM-derived brain tumor stem cells (BTSCs) [169] and inhibition of STAT3 either by pharmacological agent or by gene knockdown resulted in reduced BTSC survival regardless of endogenous MGMT promoter methylation or EGFR, PTEN, and TP53 mutational status [170].