In this well-characterized genetically engineered mouse model of breast cancer, an activated ErbB2 mutant encoded by the transgenic rat c-ErbB2/neu allele under the control of the MMTV promoter drives the formation of metastatic multifocal mammary tumors at approximately 20 weeks of age [38] (Additional file 4: Fig. S8a). Here, ERBB2 is linked to breast cancer.