ESR1 and breast cancer: Recent advances in systemic therapies for early-stage breast cancer—including CDK 4/6 inhibitors for ER+/HER2−, PARP inhibitors for patients with germline BRCA mutations, adjuvant ADCs for residual disease in HER2+ breast cancer, and perioperative immunotherapy such as pembrolizumab for TNBC—have advanced management for prevention of recurrent breast cancer.65, , –68 However, their effects on ovarian function and fertility in YWBC are poorly understood.