Real-World Outcomes of First-Line Palbociclib Plus Endocrine Therapy for HR+/HER2- Metastatic Breast Cancer in Japan:...

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 poor-performance 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.

We retrospectively analyzed 46 consecutive Asian patients with recurrent or de novo HR+/HER2- breast cancer treated with first-line palbociclib 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 (<70 vs. ≥70 years) and performance status (PS; 0-1 vs. 2-3).

The median PFS was 26.6 months (range, 1.4-69.5). Stratified by age, median PFS was 26.9 months in patients <70 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.

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.