ESR1 and breast cancer: As per the US Food and Drug Administration (FDA) and European Medicine Agency (EMA) product information, fulvestrant has been approved and indicated in treating postmenopausal women with ER+, advanced or metastatic BC, either for disease relapse, on or after adjuvant antiestrogen therapy or for disease progression following endocrine therapy.34, 35 In China, fulvestrant has been launched as first‐line therapy for late‐stage BC, metastatic disease.36