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. This evidence concerns the gene ERBB2 and breast cancer.