ESR1 and breast cancer: Gallen International Expert Consensus proposed a new classification system including Luminal A, Luminal B with HER2-, Luminal B with HER2+, HER2-enriched, and triple-negative (TN) for breast cancers based on the four immunohistochemical indices: estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki671.