Based on gene expression arrays, breast cancers are classified into five majormolecular subtypes: luminal A and B, basal, HER2 (Human Epidermal GrowthFactor Receptor 2) positive and normal-like (Perou et al., 2000; Sorlie et al., 2003); other defined subtypeshave also been identified in these studies including the interferon-rich, claudinlow, and molecular apocrine (Farmer etal., 2005; Prat etal., 2010; Eroles etal., 2012). The gene discussed is ERBB2; the disease is breast cancer.