This is a multicenter, multi-arm, biomarker-stratified trial designed to evaluate biomarker-directed therapies in patients with estrogen receptor-positive/hormone receptor-negative (ER+/HR-) and triple-negative (TN) metastatic breast cancer (MBC). The trial integrates both retrospective and prospective data collection, including archival tumor tissue, medical record abstraction, and prospective tumor and blood sampling prior to initiation of protocol directed treatment. Based on biomarker subtype, participants will receive standard of care therapy. Liquid biopsy will be collected on Cycle 2 Day 1, and then liquid biopsy, imaging and clinical data will be collected at each re-staging. Treatment will continue until discontinuation for progression, toxicity or at the discretion of the treating physician.
