e21563 Background: Osimertinib is standard of care for patients with advanced non–small-cell lung cancer (NSCLC) carrying acquired epidermal growth factor receptor ( EGFR) T790M mutation. However, few studies have been conducted to investigate the impact of rebiopsy on clinical outcomes after resistance to osimertinib. We evaluated whether next-generation sequencing (NGS) of tissue and liquid rebiopsy could favor post-progression outcomes of T790M-positive advanced NSCLC patients treated with osimertinib. Methods: Immediately just after resistance to second- or further-line osimertinib, advanced NSCLC patients with acquired EGFR T790M mutation were retrospectively divided into the NGS and non-NGS groups according to whether they underwent NGS of tissue or liquid rebiopsy. The co-primary endpoints were post-progression survival (PPS) defined as the time from osimertinib resistance to subsequent-line treatment resistance, and post-progression overall survival (pOS) defined as from osimertinib resistance to death or end of the last follow-up. Multivariable analyses were done using Cox proportional hazards regression model and log-rank test. Results: Between January 2017 and July 2019, 89 patients (62 vs. 27 for the NGS and non-NGS groups respectively) were eligible for final analyses. In the NGS group, 3.2% (2/62) underwent tissue rebiopsy only, 29.0% (18/62)only had liquid rebiopsy, and 66.8% (42/62)with both tissue and liquid rebiopsy.The NGS group received more targeted or combined therapy after resistance to osimertinib (62.9% vs. 40.8%, P= 0.053). The NGS group was significantly superior to the non-NGS group in the co-primary endpoints. The median PPS was 6.1 vs. 2.7 months (hazard ratio [HR], 0.49; 95%CI, 0.30 to 0.80; 2-sided log-rank P= 0.004). Meanwhile, the median pOS was 11.7 vs. 6.8 months (HR, 0.50; 95%CI, 0.29 to 0.85, 2-sided log-rank P= 0.009). Conclusions: Providing more opportunities for individualized treatment, NGS of tissue and liquid rebiopsy favors post-progression outcomes of EGFR T790M-positive advanced NSCLC patients treated with osimertinib.
P3.02b-032 Association between EGFR T790M Mutation Copy Numbers in Cell-Free Plasma DNA and Response to Osimertinib in Advanced NSCLC
