Claudin-7 is a protein that in humans is encoded by the CLDN7 gene. It belongs to the group of claudins.Claudins, such as CLDN7, are involved in the formation of tight junctions between epithelial cells. Tight junctions restrict lateral diffusion of lipids and membrane proteins, and thereby physically define the border between the apical and basolateral compartments of epithelial cells. It is expressed in kidney, lung and prostate. Claudin-7 is down-regulated in breast cancers, including ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS) and invasive ductal carcinoma (IDC), as well as in several cancer cell lines. Loss of expression correlates with histological grade, occurring predominantly in high-grade lesions.