Signatera-Guided CDK4/6 Inhibitor Therapy in Breast Cancer

Circulating tumor DNA testing using Signatera Genome assay is performed every 3 months for up to 4 years to guide timing of CDK4/6 inhibitor initiation. Participants with positive ctDNA results initiate CDK4/6 inhibitor therapy (ribociclib or abemaciclib) plus standard endocrine therapy for a minimum of 2 years. Participants with negative ctDNA results continue endocrine therapy alone with ongoing surveillance. CDK4/6 inhibitor selection and endocrine therapy regimen per the physician's choice following standard-of-care guidelines.