Liquid-Biopsy-Based Identification of EGFR T790M Mutation-Mediated Resistance to Afatinib Treatment in Patients with Advanced EGFR Mutation-Positive NSCLC, and Subsequent Response to Osimertinib.

BACKGROUND: Acquired epidermal growth factor receptor (EGFR) T790M mutation is the primary resistance mechanism to first-generation EGFR tyrosine kinase inhibitors (TKIs) used in advanced, EGFR mutation-positive non-small-cell lung cancer (NSCLC). Available data, predominantly in Asian patients, suggest that this mutation is also the major cause of resistance to the irreversible ErbB family blocker, afatinib. For EGFR T790M-positive patients who progress on EGFR TKI therapy, osimertinib is an effective treatment option. However, data on osimertinib use after afatinib are, to date, scarce. OBJECTIVE: To identify the prevalence of EGFR T790M mutations in predominantly Caucasian patients with stage IV EGFR mutation-positive NSCLC who progressed on afatinib, and to investigate the subsequent response to osimertinib. PATIENTS AND METHODS: In this single-center, retrospective analysis, EGFR T790M mutation status after afatinib failure was assessed using liquid biopsy and tissue rebiopsy. EGFR T790M-positive patients subsequently received osimertinib. RESULTS: Sixty-seven patients received afatinib in the first-, second-, or third-line (80.6%, 14.9%, and 4.5%, respectively). After afatinib failure, the T790M mutation was identified in 49 patients (73.1%). Liquid biopsy and tissue rebiopsy were concordant in 79.4% of cases. All patients with T790M-positive tumors received osimertinib (73.5% after first-line afatinib); 37 (75.5%) of these had an objective response (complete response: 22.4%; partial response: 53.1%). Response rate was independent of T790M copy number. CONCLUSION: EGFR T790M mutation is a major mechanism of acquired resistance to afatinib. Osimertinib confers high response rates after afatinib failure in EGFR T790M-positive patients and its use in sequence potentially allows extended chemotherapy-free treatment.