ERBB2 and breast cancer: The four breast cancer subtypes are: (1) luminal A (ER+/PR+/HER−), (2) luminal B (ER+/PR+/−/HER2+), (3) HER2-enriched (ER−/PR−/HER2+), and triple-negative breast cancer (ER−/PR−/HER2−, TNBC); these breast cancer subtypes are used to identify targeted therapeutic treatment and potential prevention options.