Abstract
PURPOSE: Epidermal growth factor receptor (EGFR) exon 20 insertion mutations account for approximately 4% of all EGFR mutations. Given the rarity of this mutation, its clinical outcomes are not fully established. MATERIALS AND METHODS: Between 2009 and 2017, non-small cell lung cancer (NSCLC) patients who showed an exon 20 insertion were retrospectively reviewed for clinical characteristics and outcomes, including responses to chemotherapy (CTx) or targeted therapy. RESULTS: Of 3,539 NSCLC patients who harbored an activating EGFR mutation, 56 (1.6%) had an exon 20 insertion. Of the advanced NSCLC patients, 27 of 1,479 (1.8%) had an exon 20 insertion. The median overall survival was 29.4 months (95% confidence interval 9.3 to 49.6) for 27 advancedNSCLC patients. The 22 patientswho received systemic CTx achieved a 50.0% response rate and a 77.2% disease control rate, with 4.2 months of progressionfree survival. Six patients received EGFR tyrosine kinase inhibitors (TKIs). Three of the four patients that had only an exon 20 insertion showed progressive disease, while one showed stable disease. The othertwo patients had an exon 20 insertion and another EGFR mutation and achieved a partial response. CONCLUSION: The incidence of an exon 20 insertion mutation is rare in Korea and occasionally accompanied by other common EGFR mutations. Although the response to systemic CTx. in these patients is comparable to that of patients with other mutations, the response rate to firstor second-generation EGFR TKIs is quite low. Therefore, the development of a more efficient agent is urgently needed.