The meta-analysis and pooled analysis indicated that both GSTM1 null genotype (null vs. present: OR = 2.66; 95%CI = 2.19–3.14) and GSTT1 null genotype (null vs. present: OR = 2.46; 95%CI = 1.83–3.32) were associated with an increased cancer risk in smokers (Table 2). Here, GSTM1 is linked to cancer.