ERBB2 and breast cancer: Breast cancer is the malignant tumor with the highest incidence rate and the highest number of deaths among women worldwide, seriously threatening women’s physical and mental health.[1] Hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2−) breast cancers account for up to 70% of all breast cancers.[2] The main first-line therapeutic strategies for patients with HR+/HER2− breast cancers are chemotherapy and endocrine therapy (ET).