For the association between null genotype of GSTM1 polymorphisms and oral cancer risk, the results were also not conclusive.25–31,33,34,41,44,63,65,66,68,73,74 Our meta-analysis demonstrated that null genotype of GSTM1 polymorphisms was significantly associated with overall risk of oral cancer. This evidence concerns the gene GSTM1 and lip and oral cavity carcinoma.