The association between the loss of claudin-3 and claudin-4 and the degree of malignancy of ovarian cancer is in line with the known disruption of TJ function during tumorigenesis, and may explain the relationship between the claudin-low subtype with low expression of claudin-3, -4 and -7 and E-cadherin and the aggressive phenotype of breast cancer [11,12]. This evidence concerns the gene CLDN4 and breast cancer.