CYP1A1 and esophageal squamous cell carcinoma: For example, genetic variations, including CYP2E1 c1/c1 allele, GSTM1 and GSTT1 non-null genotype and EPHX slow allele, were associated with increased risk of ESCC, while CYP1A1 3' polymorphism (variant allele) may be one of the protective factors for ESCC [22,23].