Loss of expression and/or abnormal function of E-cadherin increase the ability of cells to invade neighbouring tissues, thus favouring mammary tumour progression and spread [4,13,33-35], whereas overexpression of P-cadherin is related to increased cell proliferation, motility, invasiveness, and metastatic progression, thus being considered an invasion-promoting protein in breast cancer [5,22,25,26,36-38]. The gene discussed is CDH1; the disease is breast cancer.