Several strategies for inhibiting the estrogen axis in breast cancer exist, including: selective ER modulators such as tamoxifen and raloxifene, which act as selective tissue-specific antagonists of ER in the breast [9]; selective ER degraders such as fulvestrant, which promote ER turnover [10]; and aromatase inhibitors such as exemestane (steroidal aromatase inhibitors), anastazole and letrazole (nonsteroidal aromatase inhibitors) – agents primarily used in postmenopausal women with ER-positive breast cancer – which inhibit estrogen biosynthesis [11]. Here, ESR1 is linked to breast cancer.