GSTM1 and lip and oral cavity carcinoma: The GSTM1 null genotype have increased oral cancer risk by 2.52 -fold (95% CI, 1.50–4.22; P = 0.0003) as null genotypes of this class gene have been linked with number of cancers, likely due to an increased susceptibility to environmental toxins and carcinogens, whereas the risk association of GSTT1 null genotype with OSCC found to be statistically significant (OR, 2.35; 95% CI, 1.38–4.01; P = 0.001) (Table 2).