Treatment Sequencing of CDK4/6 Inhibitors in Bone-Only Hormone Receptor-Positive Metastatic Breast Cancer: Multi-Center Real-World Data Revealing a Numerical Trend Favoring Later-Line Use

Abstract

Simple Summary Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy are standard first-line treatments for hormone receptor-positive (HR+), HER2-negative metastatic breast cancer (MBC). However, the optimal sequencing of CDK4/6i for patients presenting with bone-only disease (BoD) remains unclear. In this multi-center retrospective study of 282 patients with baseline BoD, we compared progression-free survival (PFS) and overall survival (OS) between patients receiving CDK4/6i in first-line versus second- or later-line settings. While first-line use showed a trend toward longer PFS, later-line use showed a numerical trend toward longer OS, which lost statistical significance in multivariate analysis. These real-world findings highlight the need for personalized treatment sequencing in HR+/HER2− MBC patients presenting with bone-only metastasis.