ERBB2 and breast cancer: We have found that normal mouse or rat tissues exhibit nearly undetectable levels of Cks1 protein, whereas both Cks1 mRNA and protein levels are very high in corresponding tumor tissues derived from mammary tumors excised from different murine models of mammary tumorigenseis (erbB2, c-myc and polyoma middle-T (PyMT) driven transgenic mice) and in carcinogen-initiated rat models [110].