CYP2C19 and esophageal squamous cell carcinoma: CYP2C19*3 has a premature stop codon in exon 4 and it is biologically plausible that the CYP2C19*3 polymorphism is a modulator of cancer susceptibility; however, we did not find CYP2C19*3 to be associated with ESCC susceptibility in our study population.