We evaluated outcomes between osimertinib and first/second-generation (1G/2G) EGFR-tyrosine kinase inhibitors (TKIs) as first-line (1L), and investigated how T790M status and sequential osimertinib after 1G/2G EGFR-TKI failure affected overall survival (OS).<h4>Materials and methods</h4>We retrospectively evaluated the outcomes of patients with advanced NSCLC harboring exon 19 deletion or L858R mutation who received osimertinib and 1G/2G EGFR-TKIs as 1L treatment from January 2015 to March 2021. Here, EGFR is linked to non-small cell lung carcinoma.