EGFR and non-small cell lung carcinoma: To investigate the molecular mechanisms involved in the resistance of NSCLC cells exposed to suboptimal doses of EGFR-TKIs, we treated two NSCLC cell lines carrying an EGFR exon 19 deletion (HCC827 and PC9) with low doses of gefitinib, using two drug regimens, continuous and intermittent, to obtain gefitinib-resistant (GR)-Low and GR-Pulse cells, respectively.