Investigating Novel Resistance Mechanisms To Third Generation Egfr Tki Osimertinib In Non-Small Cell Lung Cancer Patients Using Next Generation Sequencing.

2572Background: Third generation epithelial growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) osimertinib (AZD9291) has proven effective in Non-small cell lung cancer (NSCLC) patients who have developed EGFR T790M-mediated resistance to other EGFR TKIs. Unfortunately, a majority of patients still undergo progressed disease after receiving osimertinib treatment. Acquired EGFR C797S mutation has been identified as one major mechanism; however, resistance mechanisms of remaining cases are still largely unknown. Methods: Using next generation sequencing (NGS) targeting 416 cancer-relevant genes, we analyzed the mutation profiles of 99 NSCLC patients that were clinically resistant to osimertinib. Results: In addition to the notable EGFR C797 variants (22%), L792 mutations were identified in 10% of patients, and a further 7% cases carry L718 mutations. Further analysis of 14 patients with paired pre-treatment samples confirmed that these EGFR mutations were acquired during treatment. Interestingly, ...