In our multi-institutional cohort (N = 200), E746_A750del was associated with significantly prolonged progression-free survival (PFS) with 1L osimertinib versus L747_A750>P [median 21.3 months (95% confidence interval, 17.0–31.7) vs. 11.7 months (10.8–29.4); adjusted HR 0.52 (0.28–0.98); P = 0.043].