CDK4/6 inhibitor therapy in hormone receptor-positive metastatic breast cancer patients: A single-center experience

Breast cancer represents the most frequently diagnosed malignancy among women worldwide. Hormone receptor (HR)-positive breast cancer constitutes approximately 60–75% of all breast cancer cases. In patients with HR-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer, endocrine therapy remains the preferred first-line treatment approach. Therapeutic strategies for these patients include estrogen receptor modulators, estrogen receptor antagonists, aromatase inhibitors, and cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, which target cell cycle regulation. In recent years, an expanding body of evidence has highlighted the safety and efficacy of CDK4/6 inhibitors. Accordingly, the present study aimed to retrospectively evaluate the clinical characteristics of patients with metastatic breast cancer who were managed with CDK4/6 inhibitors at the Düzce University Oncology Clinic between January 2019 and January 2025.