ESR1 and breast cancer: Gallen International Expert Consensus meeting [1], breast cancers are divided into 4 subtypes including luminal A-like, luminal B-like, human epidermal receptor-2 (HER-2) positive and triple-negative breast cancer (TNBC) based on immunohistochemistry (IHC) tests for estrogen receptor (ER), progesterone receptor (PR), ki67 together with IHC or in situ hybridization (ISH) tests for HER-2 amplification.