Clinical outcomes and treatment strategies of CDK4/6 inhibitors combined with endocrine therapy in HR-positive advanced breast cancer: A retrospective study from a single center.

e13072 Background: CDK4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) have emerged as a cornerstone treatment for hormone receptor-positive, HER2-negative (HR+/HER2-) advanced breast cancer (ABC). This study seeks to assess the real-world effectiveness and safety of the CDK4/6i and ET combination in patients with HR+/HER2- ABC. Methods: A retrospective analysis was performed on the clinicopathological features, treatment details, survival outcomes, and safety data of HR+/HER2- advanced breast cancer (ABC) patients treated with CDK4/6 inhibitors in combination with endocrine therapy at a single center from January 2022 to August 2024. The primary endpoint was progression-free survival (PFS), with secondary endpoints including overall response rate (ORR), disease control rate (DCR), and the occurrence of adverse events (AEs). Results: A total of 864 eligible patients were included in the study (median age: 51 years). The median progression-free survival (mPFS) for the overall cohort was 29.0 months (95% CI: 23.1–32.0 months). For ET-sensitive patients who received first-line CDK4/6i treatment, the mPFS reached 46.9 months. Subgroup analysis indicated that patients with visceral metastases had an mPFS of 20.0 months following treatment with CDK4/6i and ET, with liver and brain metastases identified as independent prognostic factors for poorer outcomes. The most common AEs associated with the combination treatment were hematologic toxicities, including neutropenia (96.3%) and leukopenia (94.3%). No significant difference in overall therapeutic benefit (PFS2) was observed between the two groups of patients who received sequential chemotherapy or CDK4/6i as first- or second-line treatments. Following progression on CDK4/6i, 55.3% of patients continued with ET in combination with other agents, showing favorable therapeutic outcomes. Conclusions: This study offers real-world evidence demonstrating the effectiveness and safety of CDK4/6i in combination with ET for HR+/HER2- advanced breast cancer. It underscores the significance of early treatment and the necessity for personalized treatment plans tailored to metastatic burden and patient tolerability.