EGFR and lung cancer: Increased copy number of the EGFR gene has been reported to be associated with increased response to EGFR-TKI therapy, PFS and OS.[28,29] Copy number gain of the EGFR gene is associated with EGFR mutations in lung cancer cells[30] and tissues.[31] As the result, increased copy number of the EGFR gene may cause increased mutant EGFR DNA contents in EGFR mutation lung cancer tissues in our study.