Use of Metronomic Chemotherapy in Hormone Receptor-Positive/HER2-Negative Metastatic Breast Cancer: A Retrospective Multicenter Study

Purpose

The optimal chemotherapy strategy after progression on cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer remains a matter of controversy. This study evaluated the efficacy of metronomic chemotherapy compared with other post-CDK4/6i treatment strategies in a real-world setting. Patients and methods: This retrospective multicenter study included patients with HR+/HER2- metastatic breast cancer progressing on CDK4/6i plus endocrine therapy and subsequently treated with systemic therapy. Progression-free survival (PFS) was the primary endpoint. Secondary endpoints included overall survival (OS), objective response rate (ORR), clinical benefit rate (CBR), and safety. Propensity score matching (1:2) was performed to reduce selection bias.