FHIT and esophageal squamous cell carcinoma: Many tumor suppressor genes (TSGs), such as CDKN2A, FHIT, MGMT, RASSF1A, CDH1 and APC, have been reported to be silenced by promoter hypermethylation in the development of breast cancer [13], lung cancer[14, 15], thymic epithelial tumors[16], colorectal cancer[17, 18] and ESCC [19].