Circulating Tumor Cell Dynamics after CDK4/6 Inhibitor for Hormone Receptor–Positive Metastatic Breast Cancer: A Biomarker Analysis from the PACE Phase II Study

Baseline CTC enumeration provides significant prognostic information in HR+/HER2- MBC. Stage IVaggressive patients derive greater benefit from F + P or F + P + A over fulvestrant alone, independent of clinical or ctDNA features. This highlights the potential of CTCs to guide treatment decision-making.