Real-world efficacy and safety of CDK4/6 inhibitors plus endocrine therapy in HR+/HER2 − metastatic breast cancer: a single-institution experience

Abstract Background Hormone receptor–positive, HER2-negative (HR+/HER2−) metastatic breast cancer is the most common type of advanced breast cancer. The addition of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors to endocrine therapy (ET) has made a marked change to patient outcomes. While clinical trials have established their efficacy, real-world studies like this one are needed to confirm their effectiveness given the many variables which may arise in patient demographics and clinical presentation. Methods A retrospective study was conducted on patients with HR+/HER2 − metastatic breast cancer treated with palbociclib, ribociclib, or abemaciclib plus ET at Electricity Hospital, Cairo, Egypt, between January 2019 and January 2025. Data on demographics, clinical characteristics, and treatment outcomes were collected from medical records. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan–Meier method, and prognostic variables were analyzed using Cox regression. Results A total of 59 patients (94.9% female; median age 58 years) were included. De novo metastatic disease was present in 39%, and visceral metastases in 33.9%. Ribociclib was prescribed to 52.5%, palbociclib to 39%, and abemaciclib to 8.5%. The objective response rate (ORR) was 88.1%, and the clinical benefit rate (CBR) was 98.3%. Median PFS was 23.7 months (95% CI, 11.9–23.9), and median OS was 38.9 months (95% CI, 27.0–60.3). On univariate analysis, absence of brain metastases, endocrine sensitivity, treatment response, and neutropenia were linked to longer PFS and OS. Dose reduction did not negatively impact outcomes. Toxicities were generally manageable, with grade 3–4 neutropenia in 33.9% of patients and no febrile episodes. Conclusion In this real-world cohort, CDK4/6 inhibitors plus ET achieved survival outcomes similar to those reported in clinical trials, with a favorable safety profile. Endocrine sensitivity, absence of brain metastases, and development of neutropenia were associated with better survival, supporting the use of CDK4/6 inhibitors across a broad patient population.