Subjects and methods: A descriptive cohort study was conducted in 41 patients with EGFR mutation positive stage IV non-small cell lung cancer who failed after first - and second-generation EGFR-TKIs therapy with presence of T790M resistance mutation was treated with osimertinib at Nuclear medicine and Oncology Center Bach Mai Hospital from January 2018 to the end of February 2022 and follow up until the end of August 2022.