Non-small cell lung cancers (NSCLCs) harboring uncommon epidermal growth factor receptor (EGFR) mutations are heterogeneous and show variable prevalence and clinical responses to EGFR tyrosine kinase inhibitors. We investigated the characteristics of uncommon EGFR mutations and the clinical efficacy of afatinib in patients with NSCLC harboring uncommon EGFR mutations.

In this multicenter, retrospective study, we analyzed patients with NSCLC with uncommon EGFR mutations in 16 South Korean institutes. Mutations were categorized according to their incidence: 1) major uncommon mutations (G719X and L861Q), 2) compound mutations, and 3) minor uncommon mutations (exon 20 insertion, S768I, and de novo T790M).

Of 703 patients with EGFR-mutant NSCLC, 64 (9.1%) had uncommon EGFR mutations. Afatinib demonstrated activity against tumors harboring major uncommon mutations [median time of treatment (TOT): 20.3 months, 95% confidence interval (CI)=15.1-25.5; overall survival (OS): 30.6 months, 95% CI=26.3-34.8] and compound mutations (median TOT: 12.3 months, 95% CI=7.7-17.0; OS: 29.1 months, 95% CI=20.4-37.7) but not against tumors harboring minor uncommon mutations (median TOT: 3.8 months, 95% CI=1.7-6.0; OS: 8.5 months, 95% CI=5.2-11.7). The S768I mutation was present in 14 patients (1.99%). The median TOT and OS were not significantly different between S768I mutations and resistant exon 20 mutations.

Afatinib is effective in patients with NSCLC harboring major uncommon and compound EGFR mutations.