To confirm whether the presence of mutated-EGFR was independently associated with SBM, multivariable analysis was performed. For stage IIIB-IV NSCLC patients, the presence of mutated-EGFR was significantly associated with the occurrence of SBM as compared to that of WT-EGFR (HR = 2.98, 95% CI, 1.50-5.93, P = 0.002) after adjusting age (HR = 2.00, 95% CI =1.16-3.45, P = 0.012) and other common demographic covariates (Table 3). Similar results were observed for both the exon 19 deletion-positive and the L858R point mutation-positive groups when compared to the WT-EGFR group (HR = 2.79, 95% CI, 0.36-1.25, adjusted P = 0.012 and HR = 3.08, 95% CI, 0.33-1.49, P = 0.002, respectively). Further analysis revealed that there was no difference for SBM occurrence between the exon 19 deletion and L858R point mutation groups (HR = 0.91, 95% CI, 0.47–1.74, P = 0.770).