A subset of breast carcinomas show claudin “low” expression profile (as defined by decreased gene-expression of claudins-1, -3, -4, -7, and -8 [23], or by decreased expression of claudin-3, -4, -7, E-cadherin and calcium-dependent cell-cell adhesion glycoprotein [27, 30]). Here, CLDN1 is linked to breast carcinoma.