942 primary invasive breast tumors arrayed in triplicate in TMAs were examined for the expression of a panel of IHC markers; ER, PR, HER-2, Ki67, CK5/6, EGFR, claudin 3, claudin 4, claudin 7 and E-cadherin to approximate the known molecular subtypes of breast cancer [16, 26]. Here, CLDN3 is linked to breast cancer.