ERBB2 and breast cancer: Focusing on the isoform HRGβ2, our previous studies in mice have shown that HRGβ2 overexpression, independent of estrogen stimulation or high levels of the HER2 (erbB-2) oncogene, is sufficient for the generation of adenocarcinomas while favoring the metastatic spread of breast cancer(BC) cells [14, 15].