The purpose of this study is to compare the usual treatment of chemotherapy followed by hormone therapy plus ribociclib to the study treatment of hormone therapy plus ribociclib. The study focuses on post-menopausal patients with stage II or III, estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)- negative breast cancer who have a low risk of recurrence. Ribociclib is a targeted therapy that belongs to a group of drugs called kinase inhibitors. Participants will be randomly assigned to 1 of 2 study groups. Group 1 will receive the usual treatment, which is chemotherapy followed by hormone therapy plus ribociclib. Group 2 will receive hormone therapy plus ribociclib; these patients will not receive chemotherapy. Study procedures also include physical examinations, laboratory tests, submission of tumor tissue samples, and imaging assessments.
STUDY00005155: A Phase III Trial of Rx Therapy Guided by Genomic Risk Assessment For High Anatomic Stage ER-pos/HER2-neg Breast Cancer with RS<=25