CDK4 and breast carcinoma: Additionally, because inhibitors of CDK4/6 combined with antiestrogens are approved for first-line therapy and beyond in metastatic ER+ breast cancers (Wardell et al., 2015a; Dean et al., 2010; Yang et al., 2017), we examined whether the CDK4/6 inhibitor, palbociclib, can be used in combination with BZA to enhance the inhibition of breast cancer cell proliferation.