Inclusion Criteria:  Have a diagnosis of HR+, HER2- locally advanced or metastatic breast cancer  Have radiologic evidence of disease progression or recurrence either  On treatment with a CDK4/6 inhibitor with aromatase inhibitor (AI) as initial therapy for advanced disease, or On/after treatment with a CDK4/6 inhibitor plus endocrine therapy (ET) administered as adjuvant therapy for early stage breast cancer Must be deemed appropriate for treatment with ET If female, have a postmenopausal status by natural or surgical means Have Response Evaluable Criteria in Solid Tumors (RECIST) evaluable disease (measurable disease and/or nonmeasurable disease) Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group scale (Oken et al. 1982) Have adequate renal, hematologic, and hepatic organ function Must be able to swallow capsules/tablets  Exclusion Criteria:  Have visceral crisis, lymphangitic spread, or leptomeningeal carcinomatosis Have symptomatic or untreated central nervous system metastasis Have received any systemic therapy between disease recurrence/progression and study screening Have received more than 1 line of therapy for advanced or metastatic disease. Have received prior chemotherapy for metastatic breast cancer (MBC) Have received prior treatment with fulvestrant, any investigational estrogen receptor (ER)-directed therapy (including selective ER degraders [SERDs] and non-SERDs), any phosphatidylinositol 3-kinase (PI3K)-, mammalian target of rapamycin (mTOR)-, or protein kinase B (AKT)-inhibitor