GSTM1 and hepatocellular carcinoma: Previous some studies have showed that the deficient types of GSTM1 and GSTT1, namely GSTM1-null and GSTT1-null genotypes are completely lack of respective enzyme activity and cannot metabolize transfer AFB1-epoxide, the most important metabolic carcinogen of AFB1, to un-toxic metabolite which is highly soluble and can be excreted out of body, which may be associated with the increased risk of HCC [18], [32].