The levels of CLDN3 and CLDN4 were frequently elevated in pancreatic adenocarcinoma, ovarian cancer, endometrioid adenocarcinoma, and prostate cancer [49,50,51,52], while CLDN7 has been found to be decreased in invasive ductal carcinomas of the breast [53]. Here, CLDN4 is linked to invasive ductal breast carcinoma.