After stratifying by smoking status (current, former and never smokers), the associations of rs16969968 and rs578776 on 15q25 with risk were only present in current (OR=1.39, 95%CI 1.15-1.68, P<0.001, and OR=0.68, 95%CI 0.54-0.86, P=0.001, respectively), and former smokers (OR=1.31, 95%CI 1.05-1.63, P=0.01 for rs16969968 only, Figure 2), but not in never smokers (OR=1.18, 95%CI 0.84-1.65, P=0.32 and OR=1.07, 95%CI 0.76-1.51, P=0.70, for rs16969968 and rs578776, respectively). The risk effect in smokers seemed to be constant among different levels of smoking exposure measured as CPD (Pinteraction=0.55 and Pinteraction=0.11 for rs16969968 and rs578776, respectively) and cotinine (Pinteraction=0.92 and Pinteraction=0.36 for rs16969968 and rs578776, respectively). rs4105144 and rs7937 on 19q13 were robustly associated with lung cancer risk in current smokers only after adjusting for smoking (cotinine level, CPD, duration of smoking, Table 4, Figure 2). Similarly to SNPs on 15q25, no interaction between these two SNPs and levels of CPD (Pinteraction=0.94 and Pinteraction=0.88 for rs4105144 and rs7937, respectively) and cotinine (Pinteraction=0.90 and Pinteraction=0.20 for rs4105144 and rs7937, respectively) was detected in smokers in the present study. Among current smokers adjustment for as-measured cotinine
