CLDN1 and nasopharyngeal carcinoma: Despite such controversies related to CLDN expression and function in tumorigenesis, several studies indicate that increased CLDN1, CLDN4, or CLDN7 can act as a suppressor of metastasis, and a potential inducer of MET in breast, lung, colon, pancreatic, gastric epithelial and nasopharyngeal carcinoma cells [24,34,35,36,37].