Murine mammary epithelial cells engineered to express high level of HER2 acquire early during tumor development the capacity to metastasize through a pathway involving the autocrine production of Wnt4 and RANKL: Wnt4 supports cell proliferation, survival, and tumorigenesis of breast cancer cells; RANKL supports the survival of metastatic cells [380,381]. This evidence concerns the gene ERBB2 and breast cancer.