CDK4 and breast cancer: Among the discrepant genes between cell lines and primary breast tumors; one gene (CDKN2D, cyclin dependent inhibitor 2D, inhibits CDK4) is up regulated in three high HER2 expressing breast cancer cell lines and down regulated in HER2+ expressing breast carcinomas whereas, two other genes (CNOT2, PAPSS2) are down regulated in HER2 expressing cell lines and up regulated in HER2 overexpressing breast cancer tissues.