Clinical outcomes of EGFR exon 20 insertion mutations in advanced non-small cell lung cancer in Korea

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 advanced NSCLC patients. The 22 patients who received systemic CTx achieved a 50.0% response rate and a 77.2% disease control rate, with 4.2 months of progression-free 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 other two 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 first- or second-generation EGFR TKIs is quite low. Therefore, the development of a more efficient agent is urgently needed.