Real-World Outcomes of Palbociclib with Endocrine Therapy in HR+/HER2- Metastatic Breast Cancer: A Retrospective...

Background: Hormone receptor-positive (HR+), Human Epidermal growth factor Receptor 2 (HER2-negative) metastatic breast cancer (MBC) represents a substantial proportion of breast cancer cases in Saudi Arabia. Despite the established efficacy of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, particularly Palbociclib, in randomized control trials, real-world data from local institutions in Saudi Arabia remain limited. Objectives: This study aimed to evaluate progression-free survival (PFS), overall survival (OS), and toxicity profile among HR+, HER2-negative MBC female patients treated with Palbociclib at King Fahad Medical City (KFMC). Methods: A retrospective study was conducted on female patients with HR+/HER2-negative MBC treated with oral palbociclib combined with endocrine therapy (ET) at KFMC between January 2021 and September 2024. Data were collected from electronic health records. Descriptive statistics were conducted using mean for continuous variables and frequency for categorical variables. Survival analyses were conducted using Cox regression, log-rank tests and Kaplan-Meier analysis. Results: A total of 169 female patients with HR+/HER2- MBC were included. In the first-line setting, the median PFS was 20.14 months (95% CI: 14.65-30.49), compared with 11.3 months (95% CI: 7.98-not estimable) in the second-line setting. For OS, the median OS values were 53.1 months (95% CI: 41.2-not estimable) in the first-line group and 23.7 months (95% CI: 18.5-not estimable) in the second-line group. Significant predictors of shorter PFS included age, Body Mass Index (BMI), type of ET, cancer type, line of therapy, family history of cancer, and history of VTE. Visceral metastasis (HR = 3.087; p = 0.0229) and ECOG performance status of 4 (HR = 13.86; p = 0.0156) were associated with significantly shorter OS. The most common hematological adverse events (AEs) were neutropenia (45.6%), followed by anemia (5.9%), leukopenia (5.3%), and back pain (5.3%). Most toxicities were managed with dose reduction, holding treatment, or supportive care. Conclusions: Palbociclib demonstrated favorable survival outcomes and a manageable safety profile, with neutropenia being the most common AE. This study provides region-specific real-world evidence supporting the use of Palbociclib in HR+/HER2- MBC. These findings align with global trial data and highlight the importance of individualized treatment in clinical practice.