BACKGROUND. EGFR gene mutations have been reported in 15–60% of non-small cell lung cancers (NSCLCs) with an important difference in prevalence between Eastern and Western populations. 1,2 The most common EGFR-activating mutations in NSCLC include in-frame deletions in exon 19 and a substitution in exon 21 (L858R) which account for 47% and 41%, respectively, of observed EGFR mutations in ...