Tamoxifen has long been an established adjuvant treatment in the management of advanced breast cancer. Studies carried out by the National Surgical Adjuvant Breast and Bowel Project (NSABP) and other groups also established its use in the treatment of early breast cancer and subsequently as a risk-reducing agent for the development of contralateral breast cancer in breast cancer patients. The NSABP began its investigation of tamoxifen as a preventive agent in the early 1990s in women who had never had the disease with its Breast Cancer Prevention Trial (P-1). Its second prevention study, the STAR trial, is currently under way.