EGFR and glioblastoma: With systematic evaluation of IHC stains, several authors showed that while endothelial cells do not express EGFR, regional differences in EGFR staining in GBM tumor cells may be explained by different levels of EGFR amplification [45,46], with higher EGFR amplification being associated with high proliferative activity, higher mutational burden, and shorter OS [45].