Patients were selected from the lung cancer databases of Taipei Medical University Hospital (TMUH) and Wan Fang Hospital (WFH). Both TMUH, a teaching hospital, and WFH, a medical center, are run by Taipei Medical University. Patients were excluded if they had more than one primary cancer. Patients with stage I-IV NSCLC (including squamous cell carcinoma, adenocarcinoma, NSCLC-not otherwise specified and large cell carcinoma) that was histologically or cytologically confirmed between January 2006 and January 2012 (a total of 596, 382 cases from TMUH, 214 ones from WFH), and who had confirmed results from EGFR mutation testing were eligible for data collection by retrospective chart review (a total of 384, 195 cases from TMUH, 189 ones from WFH), with a data cutoff of August 2014 for outcome-SBM. This study was conducted with the approval of the Joint Institutional Review Board of Taipei Medical University (Approved number 201108006). Informed patient consent was obtained. The presence of BM was defined as previously described  (Supplementary Materials and Methods). EGFR exon 18-21 mutations were determined using direct DNA sequencing, as previously described  (Supplementary Materials and Methods). Patients with any or a combination of detectable EGFR exon 18-21 mutations, including common (exon 19 deletion and L858R point mutation), uncommon mutations (eg., exon 20 insertion, exon 18 mutation) and compound mutation (eg., exon 18/20), were placed into the mutated-EGFR group, and patients with no detectable mutated-EGFRs were put into the WT-EGFR group.