BRCA1 and esophageal squamous cell carcinoma: Tobacco chewing had 4.84, 5.69, 5.28 and 6.27 folds increased risk, and smoking had 5.14, 2.67, 2.63 and 2.84 folds risk of ESCC with promoter hypermethylation of p16, DAPK, GSTP1 and BRCA1 genes respectively.