Neoadjuvant Endocrine Therapy Combined With Chemotherapy in ER-positive, HER2-negative Stage I-III Breast Cancer

The investigators assessed radiological response with contrast-enhanced breast magnetic resonance imaging (MRI) at baseline, after four cycles of therapy, and after neoadjuvant treatment but before surgery. Best radiological response was classified according to the RECIST version 1.1. Best percentage tumour reduction was the largest reduction in target-lesion size from baseline across serial MRI examinations. Positive values denoted shrinkage; negative values denoted growth. The investigators scheduled definitive surgery about 3-6 weeks after neoadjuvant therapy, once treatment-related toxicities had resolved adequately and the patient was medically fit. A multidisciplinary team chose the type and extent of surgery after considering pretreatment disease characteristics, radiological response, patient preference, and surgical feasibility. Dedicated breast pathologists reviewed the pretreatment core-needle biopsies and postoperative surgical specimens according to institutional practice. They graded pathological response with the Miller-Payne system and recorded residual invasive tumour size and postoperative pathological stage (ypT and ypN). They assessed estrogen receptor (ER), progesterone receptor (PR), HER2, and Ki67 by immunohistochemistry using standardized institutional procedures. The treating team selected postoperative radiotherapy, endocrine therapy, and other systemic treatment according to pathological findings, recurrence risk, and current institutional and national guidelines. Follow-up then continued according to institutional practice until the predefined data cut-off of 15 July 2026.