GSTM1 and viral infectious disease: Chen et al [19] evaluating the reason for the lack of association between GSTM1 null genotypes and cervical cancer risk in their epidemiological study demonstrated that viral infection could have potential effect on the activity of xenobiotic metabolizing enzymes, particularly GSTM1. The results of their study raised a question of how chronic viral infections could affect cellular defenses against carcinogens in general.