Efficacy of EGFR-Tyrosine Kinase Inhibitors for advanced non-small cell lung cancer patients harboring rare EGFR mutations of exon 18 E709X

EGFR-tyrosine kinase inhibitors (TKIs) show efficacy against lung cancer, and afatinib has been used as a standard therapy for patients with non-small cell lung cancer (NSCLC) with EGFR rare mutations such as S768I, G719X, and L861Q. However, the efficacy of EGFR-TKIs against NSCLC with EGFR rare mutations of exon 18 E709X has been less studied. The present study aimed to analyze the efficacy and safety of EGFR-TKIs in NSCLC patients with rare mutations. Our study enrolled 15 NSCLC patients with exon 18 E709X mutation who were admitted to Zhejiang Cancer Hospital. The objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and treatment-related adverse events (TRAEs) were analyzed. The ORR of the entire cohort of patients was 33.3%. The PFS of all patients with exon 18 E709X mutations was 10.9 months. The OS was not reached. The PFS of patients with exon 18 E709-T710delinsD and E709A/G/K mutations showed no significant difference (5.3 vs. 13.5 months, P = 0.238). A significant difference in OS was observed between patients with exon 18 E709-T710delinsD mutation and those with E709A/G/K mutation (12.2 months vs. not reached, P = 0.029). No significant difference in efficacy was observed between second- and third-generation TKIs for NSCLC patients with exon 18 E709X mutations (PFS: 13.5 vs. 10.9 months, P = 0.774; OS: 17.1 months vs. not reached, P = 0.072). New treatment-related adverse events were not observed. NSCLC patients with exon 18 E709X mutations may benefit from treatment with second- or third-generation EGFR-TKIs.