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). The gene discussed is ESR1; the disease is breast cancer.