Approximately 1 in 10 US women will be diagnosed with breast cancer in her lifetime. With such a high incidence, breast cancer is a serious health concern for all American women. Within the past year, clues about the function of genes associated with breast cancer have been garnered, and navel genes that may contribute to breast tumorigenesis have been discovered, In addition, unique animal models and improvements in gene expression profiling technology have given researchers new tools to address previously unanswerable questions about this disease, Curr Opin Oncol 2000, 12:521-525 (C) 2000 Lippincott Williams & Wilkins, Inc.