Real-world outcomes of ribociclib treatment in HR-positive/HER2-negative metastatic breast cancer: efficacy, safety, and prognostic factors.

BACKGROUND: This study evaluated the real-world efficacy, safety, and prognostic factors associated with progression-free survival (PFS) in patients with HR-positive/HER2-negative metastatic breast cancer treated with ribociclib. RESEARCH DESIGN AND METHODS: This retrospective single-center study included 110 patients treated with ribociclib plus endocrine therapy between January 2023 and January 2026. PFS was estimated using Kaplan-Meier analysis. Prognostic factors were assessed using Cox regression. A 3-month landmark analysis evaluated early dose modification and grade 3-4 neutropenia, and sensitivity analyses assessed model assumptions. RESULTS: Median follow-up was 35.0 months (95% CI: 30.2-39.8), and median PFS for the overall cohort was 31.0 months (95% CI: 24.5-37.5). PFS did not differ significantly between first-line and later-line ribociclib use (p = 0.148). Grade 3-4 neutropenia occurred in 36.4%, and 36.4% required dose modification. In multivariable analysis, each 10-percentage-point increase in Ki-67 was associated with shorter PFS (HR = 1.203; 95% CI: 1.007-1.436; p = 0.041). Neither early dose modification nor early grade 3-4 neutropenia was significantly associated with subsequent PFS. CONCLUSIONS: Ribociclib demonstrated clinically meaningful PFS with manageable toxicity in real-world practice. Higher Ki-67 was associated with poorer PFS, although this association was attenuated in sensitivity analysis.