In a randomized trial involving patients with non–small-cell lung cancer with mutant EGFR (T790M) in whom a tyrosine kinase inhibitor had failed, osimertinib was associated with significantly longer progression-free survival than platinum therapy plus pemetrexed. Among patients with advanced non–small-cell lung cancer with a mutant epidermal growth factor receptor (EGFR), EGFR tyrosine kinase inhibitors (TKIs) are the standard first-line therapy. 1 – 4 Despite high tumor response rates with first-line EGFR-TKIs, disease progresses in a majority of patients after 9 to 13 months of treatment. 5 – 12 At the time of progression, approximately 60% of patients (regardless of race or ethnic background) are found to have a p.Thr790Met point mutation (T790M) in the gene encoding EGFR. 13 – 16 The presence of the T790M variant reduces binding of first-generation or second-generation EGFR-TKIs to the ATP-binding pocket of EGFR, thereby reducing . . .