Study of 2 Ribociclib Doses in Combination With Aromatase Inhibitors in Women With HR+, HER2- Advanced Breast Cancer

Key inclusion criteria: * Patient has advanced (loco-regionally recurrent or metastatic) breast cancer not amenable to curative therapy. * Patient has a histologically and/or cytologically confirmed diagnosis of ER-positive and/or PgR-positive breast cancer based on the most recently analyzed tissue sample, and all tested by local laboratory. * Patient has HER2-negative breast cancer defined as a negative in situ hybridization test or an IHC status of 0, 1+ or 2+. If IHC is 2+, a negative in situ hybridization (FISH, CISH, or SISH) test is required by local laboratory testing and based on the most recently analyzed tissue sample. * Patient must have measurable disease, i.e., at least one measurable lesion according to RECIST version 1.1. (a lesion in a previously irradiated site may only be counted as a target lesion if there is clear evidence of progression since the irradiation). * Patient has an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1. * Standard 12-lead ECG values defined as the mean of the triplicate ECGs and assessed by the central laboratory: * QTcF interval at screening \< 450 ms (QT interval using Fridericia's correction) * Mean resting heart rate 50 to 90 bpm (determined from the ECG) * Women of childbearing potential (CBP), defined as all women physiologically capable of becoming pregnant, must have confirmed negative serum pregnancy test (for β-hCG) within 14 days prior to randomization. * Women of CBP must be willing to use highl…