EGFR and glioblastoma: Another major disadvantage of the orthotopic models using xenografted human GBM cell lines in rodents is that genetic alterations present in the original tumor are not often maintained, especially the overexpression or amplification of the EGFR gene that is present in approximately 40%–50% of human GBM is typically not preserved in GBM cell lines and xenografts derived thereof (6, 15–17).