The results of several studies indicate that CYP2A6 polymorphism and polymorphisms in the enzymes that encode the CYP2A6 gene and metabolize nicotine (cytochrome P450 2A6) [8,9,10] are associated with the number of cigarettes smoked per day [10,11], and moderate the relationship between cigarette smoking and smoking-related cancers such as lung cancer [11,12]. The gene discussed is CYP2A6; the disease is cancer.