ESR1 and breast cancer: In a cohort study of patients with BRCA germline-mutated breast cancer, immunohistochemical analyses showed that the luminal A-like subtype, which is strongly positive for hormone receptors (ER and/or PgR) and low-proliferative and low-grade subtypes, were more frequently observed in BRCA2-mutated (35%) than in BRCA1-mutated (9%) [102].