RecruitingDevice studyHarnessing Analysis RNA Expression and Molecular Subtype to Optimize Novel TherapY MBCAThe HARMONY trial is an interventional trial enrolling metastatic breast cancer (MBC). Current treatment of breast cancer uses clinical subtype information (e.g. hormone receptor-positive (HR+)) to help guide treatment options. Breast cancer can also be characterized by molecular subtype, but it is not known if this information is helpful in determining treatment when breast cancer has become metastatic. HARMONY will give the treating physician of each participant the molecular subtype of the tumor based on PAM50 testing. The usefulness of this information will be determined through the physician survey. Finding out the molecular subtype of each tumor also allows the investigators to determine if the molecular subtype is different from what is expected based on the clinical subtype. This study will help determine how new types of information about tumors can help choose treatments for MBC