MTHFR and esophageal squamous cell carcinoma: Here, to explore the roles and possible interactions of serum vitamin B2 and B12 concentrations, MTHFR C677T polymorphism and aberrant DNA methylation of cancer-related genes including p16 and p53 in ESCC and EPL, we carried out a molecular epidemiological study in a Chinese population with extremely high incidence of ESCC.