ERBB2 and breast cancer: Based on the presence or absence of the Hormone receptors (HRs), progesterone receptor (PR) and oestrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) breast cancer can be divided into three subtypes: HR+ (ER+/HER2−, or PR+/HER2− or ER+/PR+/HER2−), HER2+ (HR+ or HR−), and triple-negative breast cancer (TNBC, ER−/PR−/HER2−).