CHRNA3 and lung cancer: As shown in Figure S4, there were significant differences of the associations between the CHRNA3 genotypes and the increased risk of COPD as well as lung cancer in smoking status (Breslow-Day test: P = 0.043 for COPD; P = 0.002 for lung cancer) as the associations were all significant in smokers (P<0.05 for all), but not in never smokers (P>0.05 for all); and they were also significant for lung cancer risk (P = 0.028) and for COPD risk with a borderline significant (P = 0.098) in passive smokers.