Rationale and Trial Design of DAWNA-FES Trial: Single-Arm Phase II Study of Endocrine Therapy With Dalpiciclib After Progression on CDK4/6 Inhibition Based on [

Background: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have become a cornerstone in the first-line management of hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer. Despite their clinical efficacy, most patients eventually experience disease progression, and optimal treatment strategies following CDK4/6 inhibitor resistance remain unclear. Emerging evidence suggests that switching endocrine therapy (ET) while continuing cyclin inhibition may provide additional clinical benefit. Dalpiciclib, a selective CDK4/6 inhibitor, in combination with physician-selected ET, represents a potential option in this setting. Concurrently, 16α-[ Methods: This is a prospective, single-center, single-arm Phase II clinical trial evaluating the efficacy and safety of dalpiciclib plus ET in HR+/HER2- advanced breast cancer patients who progressed on prior CDK4/6 inhibitor therapy. Forty eligible patients with confirmed metastases and at least one [ Discussion: Beyond evaluating efficacy, this single-center phase II trial will provide practical insight into the feasibility of [ Ethical Approval and Trial Registration: Approved by the Ethics Committee of Peking Union Medical College Hospital (Approval number: K3629); registered at ClinicalTrials. gov (NCT05613270).