Current available endocrine therapies for ER‐positive breast cancers mainly include the selective ER modulators (SERMs, e.g. tamoxifen and fulvestrant) which exert dual agonistic or antagonistic effects on ER transcription, and aromatase inhibitors (e.g. letrozole) which inhibit oestrogen biosynthesis in postmenopausal patients 13. Here, ESR1 is linked to breast cancer.