Moreover, when Japanese Americans, a population with a high frequency of the CYP2A6 null allele, *4, were removed from our analysis, the association for higher CYP2A6 activity ratio with lung cancer risk was still statistically significant in the remaining four racial/ethnic groups (HR = 1.53; 95% CI: 1.03–2.26). Here, CYP2A6 is linked to lung cancer.