We retrospectively reviewed all the patients who had advanced or recurrent NSCLC, had initial biopsy positive for TKI sensitive mutations (either EGFR exon 19 deletion, or EGFR L858R), received first‐generation TKI treatment, developed PD, and were tested for EGFR T790M upon progression in our institution from January 2016 to September 2017. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.