In breast cancer as in other cancers on the front line of modern interdisciplinary research we have crossed the threshhold of new understanding. Fueled by an awareness that breast cancer is a leading cause of morbidity and mortality in women and honed by rapid technological advances in molecular mechanisms, major inroads into the darkness of this scourge have been accomplished during the past several years. Basic laboratory and clinical research findings must influence and in turn be influenced by efforts to detect, to diagnose and to cure the human disease. It is indeed gratifying to note that the efforts of scientists and clinicians from throughout the world reported in this volume are achieving this objective. The first section of the book focuses on the molecular and genetic basis of breast cancer. The role of specific oncogenes in mammary tumorigenesis using transgenic mice and mammary glands correlating molecular events with specific stages in neoplastic development are described and discussed. Such topics as the nature of specific oncogenes, levels of oncogene expression, the alteration of expression of other growth regulatory genes and the state of the cell in which the oncogene is expressed are specifically addressed. This section of the book is rounded out with discussions on the potential of genetic alterations as indicators of prognosis, the characterization of full-length cDNA codes for breast cancer markers and the function of antigens in tuomorigenesis.