Wang S, et al. - Researchers assessed clinical traits and outcomes in patients with primary vs acquired epidermal growth factor receptor (EGFR) T790M mutation by analyzing patient data of those diagnosed with EGFR mutation from 2012 to 2017 in Shanghai Chest Hospital. Sixty-one (1.1%) of 5,685 TKI-naive EGFR mutant patients displayed primary EGFR T790M mutation, while acquired T790M mutation was found in 98 patients of 195 TKI-treated patients. Outcomes suggest primary EGFR T790M mutation always coexists with 21L858R, while acquired T790M mutation seems to coexist with 19del. Both mutations displayed good response to osimertinib. Greater benefits from osimertinib were noted for patients with primary T790M mutation. However, during the entire clinical treatment, better overall survival was observed for patients with acquired T790M mutation.