ESR1 and metastatic malignant neoplasm in the lymph nodes: Thirdly, we didn’t have access to other key individual-level information except area, menopausal status, and study period, such as race, breast cancer sub-types, ER status, progesterone receptor (PR) status, human epidermal growth factor receptor 2 (HER2) status, and obesity associated risk factors (eg. dietary habits and physical inactivity), to examine the roles of these factors in lymph node metastasis.