 TREATMENT: Patients receive ribociclib orally PO daily on days 1-7, and doxorubicin intravenously IV on day 10. Treatment repeats every 21 days for up to 6 courses in the absence of disease progression or unacceptable toxicity. After 6 courses, patients may receive maintenance treatment with ribociclib PO daily on days 1-21. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. 