Real-world progression-free survival and overall survival of palbociclib plus endocrine therapy (ET) in Japanese patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer in the first-line or second-line setting: an observational study

Abstract Background A recent large real-world study conducted in the United States reported the effectiveness of palbociclib plus aromatase inhibitor in HR+/HER2− advanced breast cancer (ABC). However, local clinical practice and available medical treatment can vary between Japan and Western countries. Thus, it is important to investigate Japanese real-world data. This observational, multicenter study (NCT05399329) reports the interim analysis of effectiveness of palbociclib plus ET as first-line or second-line treatment for HR+/HER2− ABC by estimating real-world progression-free survival (rwPFS) and overall survival (OS) in Japanese routine clinical practice. Methods Real-world clinical outcomes and treatment patterns of palbociclib plus ET were captured using a medical record review of patients diagnosed with HR+/HER2− ABC who had received palbociclib plus ET in the first-line or second-line treatment across 20 sites in Japan. The primary endpoint was rwPFS; secondary endpoints were OS, real-world overall response rate, real-world clinical benefit rate, and chemotherapy-free survival. Results Of the 677 eligible patients, 420 and 257 patients, respectively, had received palbociclib with ET as first-line and second-line treatments. Median rwPFS (95% confidence interval) was 24.5 months (19.9–29.4) for first-line and 14.5 months (10.2–19.0) for second-line treatment groups. Median OS was not reached in the first-line group and was 46.7 months (38.8-not estimated) for the second-line group. The 36-month OS rates for de novo metastasis, treatment-free interval (TFI) ≥ 12 months, and TFI < 12 months were 80.2% (69.1–87.7), 82.0% (70.7–89.3), and 66.0% (57.9–72.9), respectively. Conclusion The addition of palbociclib to ET was effective for treating HR+/HER2− ABC in Japanese routine clinical practice.