Neoadjuvant Imlunestrant Plus Abemaciclib Treatment Guided by Ki67 Index After 2 Weeks for ER-Positive HER2-Negative Breast Cancer

This is a prospective, open-label, single-center, randomized controlled Phase II clinical study aimed at evaluating the efficacy and safety of neoadjuvant imlunestrant combined with abemaciclib guided by the Ki67 index after 2 weeks in patients with ER+/HER2- breast cancer. Eligible subjects who provide informed consent will first receive a 2-week window-of-opportunity treatment with imlunestrant combined with abemaciclib, followed by a biopsy of the primary lesion to assess Ki67 at 2 weeks. If the Ki67 of the primary lesion after 2 weeks is \<7.4%, they will be randomized in a 1:1 ratio to either Imlunestrant plus abemaciclib or neoadjuvant chemotherapy. If the Ki67 of the primary lesion after 2 weeks is ≥7.4%, patients will be assigned to neoadjuvant chemotherapy.