CDK4 and breast cancer: Patients with breast cancer, at least in part, are more vulnerable to COVID-19 infection due to a variety of reasons, including myelosuppression produced by chemotherapy given in (neo)adjuvant or metastatic settings [6], inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) [7-9], and palliative radiotherapy to the spine or pelvis.