LAUSR

e20532 Background: Missense mutations in the EGFR extracellular (EC) domain are found in 10% to 15% of glioblastomas(GBM). However, little is known about EGFR EC domain mutations in lung cancer. In this study, we retrospectively analyzed distribution of EGFR EC domain mutation in lung cancer. Methods: A total of 10100 lung cancer patients were analyzed in this study. EGFR mutations were detected by hybridization capture-based NGS panel sequencing with tumor biopsy, ctDNA or pleural effusion samples. Results: We identified gain-of-function mutations in the EC domain of EGFR in 36 (0.36%, 36/10100) patients with 23 patients carrying EGFR A289D/V/T/Y mutation, 10 patients harboring EGFR R108K/S mutation, 2 patients having EGFR T263P mutation, and 1 patient with EGFR G598R mutation. The EGFR EC domain mutation was detected in 23 patients with lung adenocarcinoma and 13 patients with other types of lung cancer (P = 0.018). Notably, 29 (80.56%) patients were detected with EGFR EC domain mutation and EGFR intracellular kinase domain (KD) mutation (P = 2.15×10-7). The incidence of L858R concomitant EC domain mutation was significantly higher compared with 19del (72.41% vs 17.24%, p = 28.64×10-5) or other EGFR KD mutations (72.41% vs 10.34%, p = 6.79×10-6). To further study whether L858R concomitant with EC domain mutation affected the efficiency of targeted therapy, we analyzed 6 patients who were treated with EGFR-TKIs. Among them, disease control rate of 2 months was 83.33% (5/6). Two patients had 10 months PFS. Three patients have been treated for 2, 5 and 12 months respectively, and are still on treatment. Conclusions: Our study reveals the distribution of EGFR EC domain mutation in lung cancer. EGFR EC domain mutation are more likely to occur concomitantly EGFR KD mutation, especial L858R. Meanwhile, our study shows that concomitant EC domain mutation and L858R may not affect the efficiency of targeted therapy.