Better survival with EGFR exon 19 than exon 21 mutations in gefitinib-treated non-small cell lung cancer patients is due to differential inhibition of downstream signals

Somatic mutations in the epidermal growth factor receptor (EGFR) kinase domain are associated with sensitivity to tyrosine kinase inhibitors (TKIs) in patients with non-small cell lung cancer (NSCLC). Our clinical data showed NSCLC patients with exon 19 deletions survived longer following gefitinib treatment than those with exon 21 point mutations. We aimed to investigate whether these two mutations produced differences in phosphorylation of EGFR and downstream signals. Two stable cell lines expressing these mutations were obtained by transfection. Inhibition of phosphorylation of EGFR, Akt, and Erk by gefitinib was detected using Western blotting, and cell inhibition tests were conducted to evaluate the bio-behavior. Gefitinib inhibited the phosphorylation of EGFR, Akt, and Erk to a greater degree in exon 19 deletion cells than in L858R cells. Gefitinib produced G1 arrest in more of the cells with exon 19 deletion than with L858R. This might be attributable to patient selection in TKIs therapy.