NOTCH1 and glioblastoma: Based on our results and those of other authors, we hypothesize that the combinations of abnormal expression and activation of growth factor receptors such as: EGFR, PDGFRα, PDGFRβ and Notch1 in GBM CSC or -derived cell lines may influence cell response to targeted therapies, thereby limiting the efficacy of single anti-EGFR or anti-PDGFR or anti-Notch1 therapies as we have seen in this study[48, 49].