CDK4 and breast cancer: This synergistic drug interaction downregulates the activity of components of the transcription apparatus and the DNA replication programme, including cdc7, CDK9, pMCM2 (S40/41), p-RNAII (S2/5), CDK4, cyclin D1 and Rb, making the combination of EGFR and cdc7/CDK9 molecular-targeted therapies promising for this subgroup of breast cancer.