ESR1 and breast carcinoma: Breast cancer is a predominant form ofcancer among western women,with an incidence of one case per eight women.1 More than 60% of breast cancers are estrogen receptor (ER)-positive.2 The standard reference for endocrine therapyrelated to this disease is based on targeting aromatase, which performsestrogen biosynthesis, or via selective estrogen receptor modulators(SERM) or degraders (SERD).