Real-world clinical outcomes associated with first-line palbociclib and aromatase inhibitor therapy among patients with HR+/HER2- advanced breast cancer in Europe.

Purpose: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is) combined with endocrine therapy is the recommended first-line (1L) treatment for hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). Real-world evidence (RWE) describing 1L CDK4/6i regimens and associated clinical outcomes in Europe is limited. The study objective was to describe clinical characteristics, tumor response, and survival outcomes in patients with HR+/HER2- ABC.

Methods: This retrospective, observational cohort study used data from 52 treatment centers in the UK, Spain, and Germany and included patients who initiated 1L palbociclib + aromatase inhibitor (AI) therapy for ABC between 2016 and 2020. Primary endpoints were real-world progression-free survival (rwPFS) and overall survival (OS).

Results: Data were abstracted from 856 patients. During treatment, complete response, partial response, or stable disease was achieved for 86.1% of patients in Spain, 80.7% in the UK, and 79.0% in Germany, while complete or partial response was achieved for 43.8% of patients in Spain, 34.9% in the UK, and 16.9% in Germany. Median rwPFS during treatment was 28.1 months for patients in Spain, 33.9 months in the UK, and 48.1 months in Germany. Median OS was 51.3 months (95% CI 46.6-NE) in the UK, 65.2 months (95% CI 65.2-NE) in Germany, and not reached in Spain.

Conclusion: This RWE supports the clinical effectiveness of 1L palbociclib + AI in routine clinical practice in European countries-consistent with the efficacy observed in clinical trials-and further supports the implementation of palbociclib-based regimens as frontline treatment of HR+/HER2- ABC.