- Participants must have histologically confirmed hormone receptor positive (HR+) HER2 negative metastatic or locally recurrent unresectable invasive breast cancer. ER, PR and HER2 measurements should be performed according to institutional guidelines, in a CLIA-approved setting. Cut-off values for positive/negative staining should be in accordance with current ASCO/CAP (American Society of Clinical Oncology/College of American Pathologists) guidelines.