ERBB2 and breast carcinoma: Prior to 2016, the mainstay of treatment for HR+/HER2– advanced breast cancer in postmenopausal women was endocrine therapy (ET) either with tamoxifen, aromatase inhibitors (AIs; anastrozole, exemestane, or letrozole) or fulvestrant (combined with ovarian suppression in premenopausal women) [2].