Subgroup analysis according to smoking status (Figure 5) showed that the pooled OR estimate of the CYP2A6*4 whole-gene deletion polymorphism remained significantly protective against lung cancer among ‘All Smoker Status’ (pooled OR=0.41; 95% CI: 0.26–0.64), ‘Mixed Smoking Status’ (pooled OR=0.39; 95% CI: 0.19–0.78) and ‘Unknown Smoking Status’. Here, CYP2A6 is linked to lung cancer.