This is a multicenter, prospective OCS designed to follow patients with locally recurrent or metastatic breast cancer in the United States. Two cohorts will be included:
- Patients with HER2-normal disease receiving their first cytotoxic chemotherapy and/or targeted therapy (1500 patients)
- Patients with HR-positive tumors receiving their first HT for advanced disease (500 patients) Patients who started their first systemic treatment for advanced breast cancer within 1 month prior to enrollment into this OCS will be eligible. A total of approximately 2000 patients will be enrolled. In order to assure that treatment patterns over time are represented in the study, the number of sites activated will be determined by projections to achieve complete enrollment over approximately 18-24 months.