Molecular Characteristics of the Uncommon EGFR Exon 21 T854A Mutation and Response to Osimertinib in Patients With Non-Small Cell Lung Cancer

Background: Epidermal growth factor receptor (EGFR) T854A is an uncommon exon 21 mutation in patients with non-small cell lung cancer (NSCLC). It was first reported in samples collected after first generation EGFR tyrosine kinase inhibitor (TKI) treatment as an acquired resistant mutation to first generation EGFR-TKI. The efficacy of osimertinib, a third generation EGFR-TKI, in these patients was not clear. Methods: In this study, a total of 8932 NSCLC patients with NGS data were retrospectively analyzed to investigate the molecular characteristics and clinical outcomes of patients with EGFR T854A mutation. Results: Eight of 8932 patients (0.09%) had EGFR T854A mutation, and 5 of them (62.5%) were treatment-naïve. Interestingly, all EGFR T854A mutations were co-occurred with EGFR L858R mutation in cis. TP53 was the most common concomitant mutation and no other driver mutation was found. Five of the 8 patients received treatment of osimertinib. Four patients achieved partial response, and one had stable disease, resulting in an overall objective response rate of 80% and disease control rate of 100%. The median progression-free survival of patients who received osimertinib was 10 months. Moreover, EGFR C797S mutation was detected in 1 patient after resistant to osimertinib treatment. Conclusion: Presence of EGFR T854A mutation was rare in NSCLC patients and our retrospective study provides clinical evidence that osimertinib may be an effective treatment to improve survival outcomes in patients with EGFR T854A.