ERBB2 and breast cancer: According to the status of the human epidermal growth factor receptor-2 (HER2) and hormone receptor (HR), BC can be divided into four subgroups: luminal A (HR+/HER2-), luminal B (HR+/HER2+), HER2-positive (HR-/HER2+), and triple-negative breast cancer (HR-/HER2- [TNBC]) (2).