Based on the status of hormone receptors such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2), breast cancers can be largely clustered into five subtypes: luminal A, luminal B (represented by the PyMT mouse model), HER2-enriched, basal-like, and normal-like40. This evidence concerns the gene ERBB2 and breast cancer.