ERBB2 and breast cancer: Based on immunohistochemical characteristics and the hormone receptor (HR) status of the disease physiology, breast cancer tumors are, hence, categorized into four primary subtypes, including HR+/HER2+ tumors that react to estrogen or progesterone and possess HER2 receptors, HR+/HER2- tumors that react to estrogen or progesterone but lack HER2 receptors, HR-/HER2+ tumors that express HER2 receptors but do not possess hormone receptors, and HR-/HER2- tumors or triple-negative breast cancer (TNBC) [37,39].