Study of MEDI-573 Plus Standard Endocrine Therapy for Women With Hormone-sensitive Metastatic Breast Cancer

This is a Phase 1b/2, multicenter, open-label study to evaluate the safety, tolerability, antitumor activity, and pharmacology of MEDI-573 in combination with an AI in adult subjects with HR+, HER2-negative MBC. This study has 2 phases: a dose-evaluation phase (Phase 1b) and a randomization phase (Phase 2).