The MDM2 protein, an oncogene product, is known to act by suppressing p53 function. Although gene amplification of MDM2 was frequently detected in human sarcomas, it was uncommon in the majority of epithelial tumors including breast cancer. However, recent reports have demonstrated that its translational activity is enhanced in a variety of carcinomas. In this report, we summarized the implications of MDM2 overexpression in human breast cancer from the literature as well as our preliminary results.