Previously, several studies have addressed the interaction between cigarette smoking and one or more of these polymorphisms on colorectal cancer risk [19,20,28-33], and some suggested an interaction between GSTT1 or GSTM1 null genotype and cigarette smoking [28,30] and between CYP1A1*2A or CYP1A1*2C and cigarette smoking [19]. The gene discussed is GSTM1; the disease is colorectal cancer.