Patients Harboring Uncommon EGFR Exon 19 Deletion-insertion Mutations Respond Well to First-generation EGFR Inhibitors and Osimeritinib Upon Acquisition of T790M
Abstract Background: This study is to investigate the effects and resistance mechanisms of first-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) in non-small cell lung cancer (NSCLC) patients carrying rare EGFR exon 19 deletion-insertion (19delins) mutations. Methods: The next generation sequencing (NGS) data of 1783 patients diagnosed as advanced NSCLC from November 2017 to September 2020 were successively and retrospectively reviewed. 41 patients with EGFR 19delins and 41 patients with EGFR exon 19 deletion (19del) were enrolled in this study, who were given first generation EGFR TKIs as first-line therapy. Results: 17 mutation types of EGFR 19delins were identified in this study, L747_P753delinsS (10/41) and L747_A750delinsP (9/41) were the most frequent mutation types, followed by L747_T751delinsP (6/41) and E746_S752delinsV (3/41). Under the same baseline characteristics, median progression-free survival (mPFS) was similar in patients with EGFR 19delins to those with EGFR 19del (10.4 months vs. 13.1 months, p=0.1076). Interestingly, patients with L747_T751delinsP had a better mPFS than those with other variants (18.7 months vs. 13.1 months, p=0.035). No significant difference in mPFS was found among the three groups of gefitinib, icotinib, and erlotinb with 14.7 months, 10.9 months, and 13.1 months (p>0.05). After progression from first-line EGFR TKIs, both EGFR 19delins and EGFR 19del had similar rates of developing resistance mechanisms including EGFR T790M mutation (45.8% vs. 57.8%). Patients acquiring T790M mutation received osimeritinib as second-line treatment, and the mPFS was similar between the groups of EGFR 19delins (n=8) and EGFR 19del (n=10): 12.0 months vs. 12.2 months (p=0.97). Conclusion: Our results indicate that patients with uncommon EGFR 19delins can also benefit from first-generation EGFR TKIs treatment, having similar treatment responses and survival outcomes to those with EGFR 19del, even similar clinical outcomes from osimeritinib upon acquiring T790M resistance mutation.