High-throughput sequencing reveals distinct genetic features and clinical implications of NSCLC with de novo and acquired EGFR T790M mutation

Introduction: De novo T790 M mutation in EGFR has been reported in various studies. However, its genetic characteristics and association with EGFR tyrosine kinase inhibitors (TKIs) treatment response remain poorly studied. Methods: We retrospectively screened 1228 consecutive non-small cell lung cancer (NSCLC) patients and identified 29 de novo T790 M carriers. Capture-based targeted deep sequencing was conducted on 21 eligible samples as well as a 20-sample cohort with acquired T790 M mutation after EGFR-TKIs treatment. We characterized and compared their mutational profiles using a panel consisting of 168 lung cancer-related genes. Results: De novo T790 M mutation was found in 5.8% of the TKI-naive patients harboring EGFR activating mutations. Among the de novo T790 M samples, T790 M was significantly more likely to coexist with L858R than with 19del (76.2% vs. 23.8%) compared to the acquired T790 M cohort (30.0% vs. 70.0%) (p = 0.003). These two groups harbored different concurrent gene mutations as well. Notably, the ratio of allele frequency (AF) of the T790 M mutation to the EGFR activating mutation in each patient, defined as the T790 M relative AF (RAF), differed significantly between the de novo and acquired T790 M cohorts (86.1% vs. 22.3%, p < 0.0001). Among the 10 patients with de novo T790 M who received the 1st-generation EGFR-TKIs treatment, interestingly, the only one who achieved partial response (PR) had the lowest T790 M RAF of 19.7%. The other 9 patients with an average T790 M RAF of 85.9% ( +/- 22.6%) achieved stable disease or progressive disease as the best response. One patient, treated with osimertinib after erlotinib failure, achieved PR and the therapeutic response sustained for more than 14.5 months. Conclusion: The molecular characteristics of de novo T790 M carriers differ distinctly from acquired T790 M carriers. The RAF of EGFR T790 M mutation may serve as a predictive biomarker for treatment response to EGFR-TKIs. Osimertinib is potentially an effective drug for the treatment of NSCLC with de novo T790 M.