CYP1B1 and head and neck squamous cell carcinoma: Singh et al. [21] study indicates a several-fold increase in cancer risk among cases that use tobacco chewing with the variant genotypes of CYP1B1*2 (OR = 8.80; 95% CI = 2.60–29.87; P < 0.05) and CYP1B1*3 (OR = 2.74; 95% CI = 1.12–6.70; P < 0.05) suggesting that interaction between genes and environment plays an important role in susceptibility to HNSCC.