Co-occurring EGFR p.E709X mutation Mediates Primary Resistance to the Third-generation EGFR-TKIs in EGFR p.G719X-mutant Patients with Advanced NSCLC

Abstract Purpose: Current NCCN guidelines recommend afatinib or osimertinib as the preferred first-line treatment strategy for patients with advanced NSCLC harboring EGFR p.G719X mutation. However, in the absence of head-to-head trials comparing afatinib with osimertinib in EGFR p.G719X mutant patients, it is unclear which regimen is the preferred treatment option. Experimental Design: A large cohort of 4228 treatment-naïve patients with lung cancer who underwent targeted NGS testing was screened for EGFR p.G719X mutation. A multicenter cohort involving 68 EGFR p.G719X-mutant patients with advanced NSCLC and NGS profiling was retrospectively enrolled to evaluate clinical responses to afatinib(n=37) and the third-generation EGFR-TKIs(n=31). Ba/F3 cells stably expressing the EGFR p.G719A mutation were created to investigate the response to EGFR-TKIs in vitro. Results: Concurrent EGFR p.E709X mutations, being the most frequent co-occurring EGFR mutation in EGFR p.G719X-mutant NSCLC(~30%), exerted a detrimental effect on outcomes in patients treated with third-generation EGFR-TKI(G719X/E709X vs. G719X; ORR:0.00% vs. 47.62%, P<0.001; mPFS:7.18 vs. 14.2 months, P=0.04; respectively). Conversely, no significant difference was found in the treatment efficacy of afatinib between EGFR p.G719X/E709X and EGFR p.G719X patients(G719X/E709X vs. G719X; ORR:71.43% vs. 56.67%, P=0.99; mPFS:14.7 vs. 15.8 months, P=0.69; respectively). In vitro experiments elucidated a resistant drug sensitivity and poor inhibition of EGFR phosphorylation in Ba/F3 cells expressing EGFR p.G719A/E709K mutation upon the third-generation EGFR-TKIs treatment. Conclusion: Co-occurring EGFR p.E709X mutation mediates primary resistance to the third-generation EGFR-TKIs in EGFR p.G719X-mutant patients but remained sensitive to afatinib. A personalized treatment strategy should be undertaken based on the co-existing EGFR p.E709X mutation status.