No significant association was found between the GSTM1 null/present variant and glioma risk of the overall population (OR=1.121(0.924-1.360); P=0.247), the Caucasian population (OR=1.260(0.966-1.643); P=0.088) and the overall mixed population (OR=0.935(0.698-1.252); P=0.651) (Figure 4a). This evidence concerns the gene GSTM1 and central nervous system cancer.