The collected clinicopathological information was presented in Table 1. Positivity of ER, PR, HER2, and Ki-67 was determined by immunohistochemical staining. HER2-positivity was defined as a 3+ immunohistochemical result or a 2+ immunohistochemical result, confirmed by fluorescence in situ hybridization. Using the histologic grade as a surrogate for Ki-67 based on the St. Gallen Expert Consensus , we approximated five breast cancer subtypes based on hormone receptor (ER and PR) status, HER2 status, and histologic grade: luminal A (ER+ or PR+/HER2−/low-intermediate grade), luminal B (ER+ or PR+/HER2−/high grade), HER2+ (ER−/PR−/HER2+), luminal HER2 (ER+ or PR+/HER2+), and triple-negative (TN) (ER−/PR−/HER2−).