EGFR and glioblastoma: Common cellular signaling pathways directed in targeted therapies have failed to improve outcomes in glioblastoma, including phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), p53 and the retinoblastoma (RB) pathway, or epidermal growth factor receptor (EGFR) gene amplification or mutation [122].