Abstract
INTRODUCTION: Osimertinib, a third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, is a first-line therapy for advanced or metastatic non-small cell lung cancer (NSCLC) with EGFR mutations, including both sensitizing and T790M resistance mutations. Its real-world efficacy against uncommon EGFR mutations remains under-researched. METHODS: The REIWA study, a multicentric, prospective, observational study conducted in Japan from September 2018 to August 2020, enrolled patients with advanced or recurrent EGFR mutation-positive NSCLC receiving osimertinib. Data on clinical outcomes, safety, disease progression, and subsequent treatments were collected for patients with uncommon EGFR mutations. RESULTS: Of 583 patients receiving osimertinib, 39 (6.7%) had an uncommon EGFR mutation. The present study included 32 of these patients after excluding seven patients with an exon 20 insertion mutation. The overall objective response rate was 53.1% [95% confidence interval (CI): 36.4-69.1], and the disease control rate was 78.1% (95% CI: 61.0-89.3). The median progression-free survival was 9.4 months (95% CI: 5.0-20.0), and the median overall survival (OS) was 21.8 (95% CI: 14.4-NA) months. Notably, patients with an exon21 L861Q mutation had a significantly longer OS than those with an exon18 G719X mutation, the respective values being 37.8 and 9.7 months (hazard ratio: 0.29; 95% CI: 0.10-0.85; P = 0.02). The rate of grade 3 or worse adverse events was 10.3%. Seven out of 32 (21.9%) patients showed progression involving only the central nervous system. CONCLUSIONS: Osimertinib demonstrated efficacy and tolerability in the clinical setting in patients with uncommon EGFR mutation-positive NSCLC.