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This single-center retrospective study assessed palbociclib plus endocrine therapy in 46 Asian patients, evaluating progression-free survival as the primary endpoint and response, disease control, and safety as secondary endpoints, with subgroup analyses by age and performance status. 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Email: keikof@nms.ac.jp](Corresponding Author: Keiko Yanagihara. Email: keikof@nms.ac.jp)\u003Cbr>Received: 28 September 2025; Accepted: 07 November 2025; Published: 30 December 2025\u003Cbr>ABSTRACT: Background: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have transformed the management of hormone receptor–positive/HER2–negative (HR+/HER2–) advanced breast cancer, yet evidence for elderly or poorperformance patients remains limited. This study examined real-world outcomes of palbociclib plus endocrine therapy in Asian patients, with additional subgroup analyses by age and performance status. Methods: We retrospectively analyzed 46 consecutive Asian patients with recurrent or de novo HR+/HER2 − breast cancer treated with first-linepalbociclib plus ET between April 2021 and March 2025 . The primary endpoint was progression-free survival (PFS) Secondary endpoints included overall response rate (ORR), disease control rate (DCR), and safety. Subgroup analyses were performed by age (\u003C70 vs. ≥70 years) and performance status (PS; 0–1 vs. 2–3) . Results: The median PFS was 26.6 months (range, 1.4–69.5) . Stratified by age, median PFS was 26.9 months in patients \u003C70 years and 26.2 months in those ≥70 years (p = 0.760). By PS, PFS was 26.9 months for PS 0–1 and 17.8 months for PS 2–3 (p = 0.099) . ORR was 60.9% and DCR 93.5%; notably, all PS 2–3 patients achieved disease control. Hematologic toxicities were common, with neutropenia (80.4%) and leukopenia (86.7%) predominating, but grade ≥ 3 anemia was rare (2.2%) . Elderly patients experienced anemia more frequently, while overall toxicity remained manageable. Dose reductions occurred in 47.8% without loss of efficacy. Conclusions: In routine Japanese practice, palbociclib plus ET provided prolonged PFS and high disease control consistent with pivotal trials and international real-world evidence. Importantly, elderly patients tolerated treatment well, and selected PS 2–3 patients also derived clinical benefit. These findings indicate that neither age nor PS alone should preclude the use of palbociclib in carefully monitored real-world patients.\u003Cbr>KEYWORDS: Metastatic breast cancer; cyclin-dependent kinase 4/6 (CDK4/6) inhibitors; real-world evidence; hormone receptor-positive; human epidermal growth factor receptor 2-negative breast cancer |  |\n\n1 Introduction  \nBreast cancer is the most frequently diagnosed malignancy among women worldwide and remains oneof the leading causes of cancer-related mortality [1] . In 2020, more than two million new cases were reported globally, with nearly 700,000 deaths. Although survival has improved with early detection and systemic therapy [1], advanced breast cancer continues to present a substantial clinical challenge.  \nCopyright © 2026 The Authors. Published by Tech Science Press.  \nThis work is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.  \nAmong breast cancer subtypes, hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2−) disease is the most common, representing more than two-thirds of cas","cbCaimLblWCyBtsq","https://ap.wps.com/l/cbCaimLblWCyBtsq","pdf",955518,15,"English","# Abstract\n# Keywords\n# Introduction","[{\"question\":\"What was the primary endpoint in this study?\",\"answer\":\"The primary endpoint was progression-free survival (PFS).\"},{\"question\":\"How were patients divided for subgroup analyses?\",\"answer\":\"Subgroups were analyzed by age (\\u003c70 vs. ≥70 years) and performance status (PS 0–1 vs. 2–3).\"},{\"question\":\"What safety and efficacy outcomes were reported overall?\",\"answer\":\"Overall response rate was 60.9% and disease control rate was 93.5%, with neutropenia and leukopenia being the most common hematologic toxicities; grade ≥3 anemia was rare (2.2%).\"},{\"question\":\"Did elderly patients and poor-performance patients benefit from treatment?\",\"answer\":\"Elderly patients showed similar PFS to non-elderly patients, and selected PS 2–3 patients achieved disease control and derived clinical benefit with manageable toxicity under monitoring.\"}]","Real-World Outcomes of First-Line Palbociclib Plus Endocrine Therapy for HR+/HER2- Metastatic Breast Cancer in Japan - A Single-Center Retrospective Study | PDF",1790710787,38]