Subsequent-abemaciclib Treatment After Disease Progression on Palbociclib in Patients With ER-positive HER2-negative Metastatic Breast Cancer

This study investigated the efficacy of continuing cyclin-dependent kinase (CDK) 4 and 6 inhibitors in patients with estrogen receptor-positive (ER+) human epidermal growth factor receptor 2-negative (HER2- ) metastatic breast cancer (MBC) after disease progression on prior-palbociclib combined with endocrine therapy (ET).This retrospective study based on 25 ER+/HER2- MBC patients reported the efficacy and predictive factors of subsequent-abemaciclib after disease progression on prior-palbociclib.The overall response rate and clinical benefit rate were 16.0% and 44.0%, respectively. The median progression-free survival (PFS) was 5.3 months. In multivariate analysis, the best overall response (BOR) to prior-palbociclib was the only independent predictive factor for PFS (p=0.015). The median time to chemotherapy was 33.9 months. The median PFS in patients treated with next-line chemotherapy after progression on subsequent-abemaciclib was 6.2 months.BOR to prior-palbociclib was the only independent predictive factor for PFS in ER+/HER2- MBC patients undergoing subsequent-abemaciclib after disease progression on prior-palbociclib.