Ribociclib and Aromatase Inhibitor in Treating Older Participants With Hormone Receptor Positive Metastatic Breast Cancer

PRIMARY OBJECTIVES: I. To estimate the safety and tolerability of the combination of ribociclib and an aromatase inhibitor in adults age 70 or older with hormone receptor positive metastatic breast cancer. SECONDARY OBJECTIVES: I. To describe the full toxicity profile including all grades. II. To estimate the rate of worst grades of myelosuppression (neutropenia, leukopenia, thrombocytopenia, and anemia), neutropenic fever, gastrointestinal (GI) side effects (nausea, diarrhea, decreased appetite, vomiting, stomatitis), fatigue, neuropathy, and thromboembolism. III. To describe rates of dose reductions, dose holds, and hospitalizations. IV. To estimate objective response rate and clinical benefit rate as defined by modified Response Evaluation Criteria in Solid Tumors (RECIST) (1.1) criteria. V. To estimate median progression-free and overall survival. EXPLORATORY OBJECTIVES: I. To estimate the rate of adherence to ribociclib. II. To explore factors other than chronologic age that can affect toxicity rates as identified using a cancer-specific geriatric assessment. III. To describe the results of the Was It Worth It (WIWI) and the results of the Overall Treatment Utility (OTU) Questionnaires. OUTLINE: Participants receive ribociclib orally (PO) once daily (QD) on days 1-21 and aromatase inhibitor per treating investigator's discretion. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, participants are followed up at 30 days, then annually thereafter.