Breast cancer remains the leading cause of death in American women 30 to 70 years of age, and research in the field of breast cancer continues at an explosive pace. Our understanding of the molecular basis of familial breast cancer has advanced significantly through investigation of the tumor suppressor geneBRCA1, as has our knowledge of the role of theATMgene and predisposition to breast cancer in ataxia-telangiectasia carriers. In addition, progress has been made in understanding the role of HER-2/neu as a prognostic factor in breast cancer. In this review, some of the recent advances in breast cancer biology that are relevant to these areas of study are highlighted.