Dalpiciclib With Endocrine Therapy for Advanced Breast Cancer After CDK4/6 Inhibitor Failure (DAWNA-FES)

CDK4/6 inhibitors are currently the standard treatment for female breast cancer patients with HR+ tumors. However, there is no established standard treatment for patients who experience treatment failure with CDK4/6 inhibitors. The MAINTAIN study has shown clinical benefits by switching to Ribociclib and changing endocrine therapy after progression on CDK4/6 inhibitors. We hypothesize that combining Dalpiciclib with physician-selected endocrine therapy, following treatment failure with CDK4/6 inhibitors, would similarly lead to improved patient survival. In this study, 18F-FES PET/CT will be employed as a non-invasive alternative to biopsy techniques for evaluating the expression of ER in various systemic lesions of the patients.