Purpose: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are the standard first-line treatment for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC); however, disease progression occurs in almost all patients and additional treatment options are needed. Herein we report outcomes of the postMONARCH trial investigating a switch in ET with/without CDK4/6 inhibition with abemaciclib after disease progression on CDK4/6i.
Methods: This double-blind, randomized Phase III study enrolled patients with disease progression on prior CDK4/6i plus aromatase inhibitor as initial therapy for advanced disease or recurrence on/after adjuvant CDK4/6i+ET.