Real-World Treatment Patterns and Outcomes of Palbociclib Plus an Aromatase Inhibitor for Metastatic Breast Cancer: Flatiron Database Analysis

Of 813 real-world patients with HR +/HER2- metastatic breast cancer, 87% initiated palbociclib at 125 mg/d and 11% discontinued due to toxicity. Median progression-free survival and time to chemotherapy were 20.0 and 36.6 months, respectively. Palbociclib initiation at 125 mg/d (vs. lower doses) was associated with improved outcomes. These findings may help clinical decision-making in patients with advanced breast cancer. Introduction: To describe real-world treatment patterns and effectiveness of first-line palbociclib plus an aromatase inhibitor (PAL+ AI) and examine the association between PAL initial dose and effectiveness among patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic/advanced breast cancer (HR + /HER2- MBC) in routine clinical practice. Patients and Methods: This retrospective analysis used Flatiron Health's database of electronic health records from > 280 cancer clinics representing > 2.4 million actively treated cancer patients in the United States. Women with HR + /HER2- MBC who received first-line PAL+ AI were included. Real-world progression-free survival (rwPFS) was defined as the time from starting PAL+ AI to death or disease progression. Real -world best tumor response (rwBTR) was assessed based on the treating clinician's assessment of radiologic evidence for change in disease burden. Results: Of 813 eligible patients, median age was 65.0 years, and median follow-up was 21.0 months. PAL was initiated at 125 mg/d and 75/100 mg/d in 86.5% and 13.5% of patients, respectively. Median duration of PAL+ AI was 16.3 months. 43.0% of patients discontinued PAL + AI; 11.0% discontinued because of toxicity. Median time to subsequent therapy and chemotherapy was 24.6 and 36.6 months, respectively. Median rwPFS was 20.0 months, and best rwBTR rate was 51.9%. Patients starting PAL at 125 versus 75/100 mg/d had longer median rwPFS (27.8 vs. 18.6 months) and higher rwBTR rate (54.0% vs. 40.4%). Conclusion: These data demonstrate the benefit of PAL+ AI in routine clinical practice and may support the initiation of palbociclib at the recommended dose of 125 mg/d for HR + /HER2- MBC. Trial Registration Number and Date of Registration: NCT04176354, November 25, 2019