CYP1A1 and lip and oral cavity carcinoma: The analysis of the metabolism pathway of PAHs and oral cancer shows a significant gene–gene interaction effect (OR: 2.220 (95% CI: 1.166–4.225), p = 0.0201), and the main effect of each SNP is not significant (p = 0.2008 and 0.8915 for CYP1A1 and GSTM1, respectively).