CHRNA5 and lung cancer: In this exploratory analysis, our main objectives were to estimate the effect size of CYP2B6 relative to CYP2A6 and CHRNA5-A3-B4 and to establish a probable independent contribution of CYP2B6 to the risk of lung cancer among smokers and in so doing implicate a role for altered nitrosamine activation in the molecular mechanism of lung carcinogenesis.