One study reported an increased risk of rectal cancer, but not of colon cancer, among former and current smokers who did not carry either CYP1A1*2A or CYP1A1*2C allele [19], while the other study showed no interaction between either of the CYP1A1 polymorphisms and smoking on colorectal cancer risk [20]. This evidence concerns the gene CYP1A1 and colonic neoplasm.