Molecular characteristics of EGFR exon 20 uncommon R776H mutation and response to osimertinib in NSCLC patients.

Abstract

e21001 Background: EGFR R776H is an uncommon exon 20 mutation in non-small cell lung cancer (NSCLC) patients. This mutation was first reported in samples after first generation EGFR TKI treatment as an acquired resistant mutation to first generation of EGFR-TKI. We further analyzed the molecular characteristics of patients with EGFR R776H mutation and its correlation with EGFR TKI therapy. Methods: In this study, a total of 16131 NSCLC patients from multiple centers with NGS data were retrospectively analyzed to study the molecular characteristics and clinical outcomes of patients with EGFR R776H mutation. Results: 44 of the 16131 patients (0.27%) had EGFR R776H mutation, and 28 of them (63.6%) were treatment-naïve while performing the mutation test. TP53 was the most common concomitant mutation in both treatment-naïve (57.1%) and treated (81.3%) patients. EGFR R776H mutation was found to coexist with multiple types EGFR mutation. The common mutations were EGFR L858R (54%) and EGFR G719A/S (25%), but It almost never coexists with 19del (2%). The coexist of EGFR R776H mutation was similar in both treatment-naïve and treated patients. In 16 of treated patients, all had received first - or second-generation EGFR TKI treatment, and the median progression-free survival (PFS) was 9 months. Interestingly, four of them found the presence of not only EGFR R776H but also EGFR T790M. It may be that EGFR R776H and T790M appear together in drug resistance, or it may be that EGFR R776H and EGFR sensitive mutation are not in the same cell clone. Two patients with EGFR R776H received treatment of Osimertinib and achieved partial response. The PFS of two patients in Osimertinib were 11 and 10 months, respectively. Moreover, EGFR C797S mutation was detected in two patients after resistant to Osimertinib. Conclusions: Presence of EGFR R776H mutation was rare in NSCLC patients and our retrospective study provides clinical evidence that Osimertinib could be of benefit and may potentially be an effective treatment strategy to improve survival outcomes in patients with EGFR R776H.