Recent studies clearly described that the interactions between HER-2/neu and cyclin D1 appear to have therapeutic relevance as several phytochemical or synthetic drugs have been demonstrated to reduce cyclin D1 expression through the inhibition of HER-2/neu, and the anti-HER-2/neu monoclonal antibody trastuzumab (Herceptin) reduces cyclin D1 protein levels in human breast cancer cells (22,23). Here, CCND1 is linked to breast cancer.