CLDN1 and cancer: Claudins, in particular, claudin-1 (CLDN1), has been frequently found to be overexpressed in primary cancers and metastasis, as well as in cancer cell lines [55,56], and the increased expression of CLDN1 was evidenced for a broad spectrum of human malignancies and cancer cell lines, including laryngeal squamous cell carcinomas (LSCCs) [57], colorectal cancer (CRC) [58], and breast and thyroid cancer [59,60,61].