Purpose: Most epidermal growth factor receptor (EGFR) exon 20 insertion (ex20ins) mutations are resistant to tyrosine kinase inhibitors (TKIs). While some non-small cell lung cancer (NSCLC) patients harboring special subtypes of EGFR  ex20ins still achieved clinical response after TKIs treatment, identifying special subtypes of EGFR  ex20ins is helpful to find out NSCLC patients who can respond to TKIs.
Case Presentation: A 71-year-old non-smoker Chinese female was diagnosed with advanced lung adenocarcinoma harboring EGFR  ex20ins (N771delinsKG). The patient received first-line afatinib (40 mg/day) therapy and a significant and substantial reduction in tumor size was observed subsequently. According to RESIST 1.1, a radiological partial response was achieved. The final progression-free survival was 10 months.
Conclusion: This is the first published case report of EGFR  N771delinsKG lung adenocarcinoma, which highlighted the heterogeneity of clinical response to TKIs for EGFR  ex20ins-mutant NSCLC. Such results need to be further investigated in prospective studies.
Keywords: afatinib, lung adenocarcinoma, EGFR  exon 20 insertions, next generation sequencing