Its subtypes are classified based on the expression status of hormone receptors (HR) and human epidermal growth factor receptor 2 (HER2), which are primarily categorized into three major groups: Luminal type (HR-positive, HER2-negative or HER2-positive), HER2 overexpression type (HR-negative, HER2-positive), and triple-negative breast cancer (HR-negative, HER2-negative). Here, ERBB2 is linked to triple-negative breast carcinoma.