GSTM1 and head and neck squamous cell carcinoma: As shown in Table 3, significant association of GSTM1 deletion with risk of HNSCC was observed in smoking group (OR = 1.51, 95% CI: 1.05–2.17, P = 0.03) but not in non-smoking group (OR = 1.14, 95% CI: 0.90–1.43, P = 0.28).