ESR1 and breast cancer: Liver biopsy confirmed metastatic carcinoma consistent with the breast cancer origin based on IHC: CK (AE1/AE3)+, ER 95% (2-3+), PR 95% (2-3+), AR 95% (3+), HER2 (c-erbB-2) 0, Ki-67 10%+, GATA-3+, and SOX10- (Figure 3A).The patient was started on OFS (GnRH agonist) + AI (exemestane) + CDK4/6 inhibitor (abemaciclib) + bone-targeting agents (zoledronic acid) as first-line treatment for HR+ HER2- metastatic breast cancer.