Combined analysis of GSTM1 and GSTT1 on HNSCC risk showed that OR of individuals with dual null genotype was elevated (OR = 1.48, 95% CI: 1.12–1.96, P = 0.006) compared to GSTM1 or GSTT1 individual null genotype (Figure 4). This evidence concerns the gene GSTM1 and head and neck squamous cell carcinoma.