Can the CDK 4/6 inhibitors be used in patients with metastatic breast cancer to the bone marrow?   

CDK 4/6 inhibitors do cause cytopenias, especially neutropenia in patients with metastatic breast cancer. Palbociclib and ribociclib cause neutropenia more frequently, and more frequently severely than abemaciclib. This would be my primary concern in treating patients with breast cancer metastasis ...