Molecular Characteristics and Clinical Outcomes of EGFR Exon 19 C-Helix Deletion in Non–Small Cell Lung Cancer and Response to EGFR TKIs

Epidermal growth factor receptor (EGFR) exon 19 deletion (E19del) is the most common activating mutation in advanced non–small cell lung cancer (NSCLC) and associates with the sensitivity of EGFR tyrosine kinase inhibitors (TKIs) treatment. However, not all mutant patterns of E19del have been well studied for the limited coverage of regular EGFR mutation testing. Here, we performed a retrospective cohort study of the C-helix E19del in advanced NSCLC patients based on the screening data by the next-generation sequencing (NGS) platform. From May 2012 to December 2019, clinical information and specimen from 7544 consecutive advanced (IIIB/IV) NSCLC patients were collected and screened for EGFR gene mutations by NGS from multicenters in China. The molecular characteristics and responsiveness to first-line EGFR TKIs therapy in NSCLC patients with C-helix E19del were analyzed. The clinical characteristics were also compared between patients with classical E19del and C-helix E19del. Thirty-eight (2.6%) patients with C-helix E19del and 1400 (97.4%) patients with classical E19dels were identified from 1438 patients with E19del. No significant difference in clinical characteristics was observed between the C-helix E19del and classical E19del groups (P > .05), except for histology (P < .001). All 22 patients with C-helix E19del as p.S752_I759del, p.A750_E758del, p.A750_E758delinsP, p.T751_A755delinsNY, p.T751_I759delinsG, p.T751_I759delinsLD, p.T751_I759delinsN, p.T751_L760delinsNL, and p.T751_D761delinsLY reached the best response as partial response rate (72.7%), and the progression-free survival (PFS) was 12.0 months. The PFS after EGFR TKIs in patients with C-helix E19del tended to be longer than patients with classical E19del but has no statistical significance (12.0 months vs 8.5 months, P = .06). The C-helix E19del could be a positive biomarker for predicting response to EGFR TKIs in advanced NSCLC patients. NGS should be the appropriate platform to identify this rare population, especially when patients harbor no actionable driver mutation initially and are reluctant to accept chemotherapy as first-line therapy.