EGF and neoplasm: By applying different EGF concentrations (0 to 20 ng/mL), we were able to generate isogenic permanent cell lines from the same tumor with stable EGFR amplification and EGFRvIII expression (>15 passages) in the absence of EGF and nonamplified, EGFRvIII-negative cell lines in the presence of 20 ng/mL EGF.