Efficacy of Palbociclib and Ribociclib in Second-line Treatment of Metastatic Hormone Receptor-positive Breast Cancer: A Single-center Experience

Objective: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors represent the standard of care for the first-line treatment for hormone receptor-positive (HR+), human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer. Increasing evidence suggests that CDK4/6 inhibitors may also be a viable option in second-line treatment. This study aimed to compare the efficacy of palbociclib and ribociclib in second-line treatment for HR+ HER2-negative metastatic breast cancer patients and to identify factors influencing treatment response. Material and Methods: We retrospectively analysed 112 patients who received either palbociclib (n=52) or ribociclib (n=60) as second-line treatment between January 2018 and December 2023 at our hospital. We evaluated demographic characteristics, clinical and pathological data, overall survival (OS), and progression-free survival (PFS), alongside factors potentially affecting these outcomes, including age, Eastern Cooperative Oncology Group (ECOG) performance status, metastasis pattern, and endocrine resistance. Results: Median PFS was 16.1 months for the palbociclib group and 20.3 months for the ribociclib group (p=0.214), while median OS was 38.1 months and 37.5 months, respectively (p=0.308). Multivariate analysis identified ECOG performance status as an independent prognostic factor (hazard ratio: 1.86, 95% confidence interval: 1.18-2.94, p=0.028). Longer PFS was observed in patients who were endocrine-sensitive or those receiving hormone therapy (25.2 months for endocrine-sensitive patients and 27.3 months after hormone therapy). Conclusion: In terms of treatment efficacy in second-line therapy, palbociclib and ribociclib are comparable. Treatment response was predominantly influenced by the patient’s performance status. These findings may guide clinicians in making treatment decisions based on individual patient characteristics.