GSTM1 and cancer: It has been hypothesisedthat lack of GSTM1 enzyme activity increases cancer susceptibility as a resultof a decreased ability to detoxify reactive intermediates of tobaccocarcinogens such as benzo[a]pyrene-7,8-diol epoxide, the activated form ofbenzo[a]pyrene [22] but the results of previous studies undertaken in oral andpharyngeal cancers are inconsistent [26, 54, 56, 57].