A Randomized, Double-Blind, Placebo-Controlled, Phase 3 Study of Nonsteroidal Aromatase Inhibitors (Anastrozole or Letrozole) plus LY2835219, a CDK4/6 Inhibitor, or Placebo in Postmenopausal Women with Hormone Receptor-Positive, HER2-Negative Locoregionally Recurrent or Metastatic Breast Cancer with No Prior Systemic Therapy in this Disease Setting

INTERVENTION: investigational material(s) Generic name etc : LY2835219 + Nonsteroidal Aromatase Inhibitors (Anastrozole or Letrozole) INN of investigational material : Therapeutic category code : 429 Other antitumor agents Dosage and Administration for Investigational material : 150 milligrams (mg) LY2835219 orally every 12 hours plus either 1 mg anastrozole or 2.5 mg letrozole orally once daily for 28 days (28 day cycles) control material(s) Generic name etc : Placebo + Nonsteroidal Aromatase Inhibitors (Anastrozole or Letrozole) INN of investigational material : Therapeutic category code : ‐‐‐ Other Dosage and Administration for Investigational material : Placebo orally every 12 hours plus either 1 mg anastrozole or 2.5 mg letrozole orally once daily for 28 days (28 day cycles) CONDITION: 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