T790M mutations have been reported to be involved in about half of the cases of resistance.9, 10 A previous study had shown the efficacy of osimertinib as second‐line treatment for T790M mutation‐positive NSCLC.11 Osimertinib was approved in 2016 for manufacture and sale in Japan for previously EGFR‐TKI‐treated EGFR T790M‐positive NSCLC and has been used in various treatment lines, not limited to the second line. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.