Claudins are integral membrane tight junction proteins which regulate paracellular permeability, maintain cell polarity, and promote cell adhesion. Claudin 3 is involved in the development of acinus and epithelial cell differentiation. In normal tissues, it is expressed on the membrane of colonic, pancreatic, and thyroid epithelium. In malignancies, it is found in epithelial ovarian cancers, pancreas, bladder, thyroid, fallopian tubes, ovary, stomach, colon, breast, uterus, and prostate carcinomas.