Choi Y, et al. - In view of the observations that exon 19 deletion and L858R mutation in exon 21 of the epidermal growth factor receptor (EGFR) are both common mutations that predict a good response to EGFR tyrosine kinase inhibitors in non–small cell lung cancer (NSCLC), researchers searched for the existence of clinically significant difference in sensitivity to EGFR tyrosine kinase inhibitors among different EGFR mutation subtypes. Among patients receiving first-line gefitinib treatment, patients with exon 19 deletion showed significantly longer median progression-free survival (PFS) and overall survival (OS) compared with those with L858R mutation and uncommon or dual mutations. Exon 19 deletion showed an independent association with favorable OS, however, male sex and primary metastatic disease were independent prognostic factors of poor OS.