This is a phase II, multicenter, open-label, single-arm clinical study. The purpose of this study is to evaluate the efficacy and safety of culmerciclib combined with anti-HER2 targeted therapy and endocrine therapy as maintenance treatment in patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer.
Culmerciclib is a novel oral cyclin-dependent kinase 2/4/6 (CDK2/4/6) inhibitor. It has been approved in China for use in combination with fulvestrant in patients with HR-positive, HER2-negative advanced breast cancer who have progressed on prior endocrine therapy.
Patients enrolled in this study will receive culmerciclib at a stepwise escalating dose of 120 mg, 150 mg, and 180 mg once daily, in combination with anti-HER2 therapy (trastuzumab with or without pertuzumab) and physician-selected endocrine therapy. Treatment will continue until disease progression, unacceptable toxicity, death, withdrawal of consent, or loss to follow-up.
The primary endpoint is progression-free survival. Secondary endpoints include objective response rate, disease control rate, clinical benefit rate, overall survival, and safety.