EGFR and non-small cell lung carcinoma: To define the underlying mechanism of acquired resistance to EGFR-TKI, we generated two osimertinib-resistant cell lines (PC-9OR, HCC827-OR) from parental NSCLC cell lines (PC-9, HCC827) that carry with activating EGFR mutation, using the dose-escalation method.21 We found both of the osimertinib-resistant cell lines were also cross resistant to gefitinib (Supplementary Fig. 1a–d).