Original article| Volume 22, ISSUE 6, P601-610, August 2022

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


      • Real-world treatment patterns and outcomes of first-line palbociclib were evaluated (n = 813).
      • Palbociclib was initiated at the recommended dose of 125 mg in 87% of patients.
      • Of 813 patients, 43% discontinued palbociclib; 11% because of toxicity.
      • Median rwPFS and time to chemotherapy were 20.0 and 36.6 months, respectively.
      • Palbociclib initiation at 125 mg was more effective than lower doses.



      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.


      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%).


      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


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