A Study of Nonsteroidal Aromatase Inhibitors Plus Abemaciclib (LY2835219) in Postmenopausal Women With Breast Cancer

Inclusion Criteria: * Have a diagnosis of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer * Have locoregionally recurrent disease not amenable to resection or radiation therapy with curative intent or metastatic disease * Have postmenopausal status * Have either measurable disease or nonmeasurable bone-only disease * Have a performance status ≤1 on the Eastern Cooperative Oncology Group (ECOG) scale * Have adequate organ function * Have discontinued previous localized radiotherapy for palliative purposes or for lytic lesions at risk of fracture prior to randomization and recovered from the acute effects of therapy * Are able to swallow capsules Exclusion Criteria: * Have visceral crisis, lymphangitic spread, or leptomeningeal carcinomatosis * Have inflammatory breast cancer * Have clinical evidence or a history of central nervous system (CNS) metastasis * Are currently receiving or have previously received endocrine therapy for locoregionally recurrent or metastatic breast cancer * Have received prior (neo)adjuvant endocrine therapy with a disease-free interval ≤12 months from completion of treatment * Are currently receiving or have previously received chemotherapy for locoregionally recurrent or metastatic breast cancer * Have received prior treatment with everolimus * Have received prior treatment with any cyclin-dependent kinase (CDK) 4/6 inhibitor (or participated in any CDK4/6 inhibitor clinical trial for which treatment assignment is still blinded) * Have initiated bisphosphonates or approved receptor activator of nuclear factor kappa-B ligand (RANK-L) targeted agents \<7 days prior to randomization * Are currently receiving an investigational drug in a clinical trial or participating in any other type of medical research judged not to be scientifically or medically compatible with this study * Have received treatment with a drug that has not received regulatory approval for any indication within 14 or 21 days of randomization for a nonmyelosuppressive or myelosuppressive agent, respectively * Have had major surgery within 14 days prior to randomization