The fight against breast cancer is expected to be effectively stimulated by interdisciplinary approaches and cross-fertilization between laboratory and clinical research findings. Of major importance, therefore, are meetings that promote rapid transfer to clinical applications of findings by basic scientists. This volume reports the proceedings of the 1991 Biennial Conference of the International Association for Breast Cancer Research and seeks to achieve this goal by presenting the most recent observations in the laboratory and their possible applications for diagnostic evaluations and clinical treatments. The sections in this book focus first on the oncogenes more likely involved in mammary tumorigenesis and on the polypeptide factors and steroid hormones affecting proliferation and possible inducing carcinogenesis in breast epithelium. A section is devoted to the epidemiological studies and to the identification of risk factors; a way to select populations at higher risk and, possibly, to help in preventing the disease. Special emphasis is given to the establishment of diagnostic criteria and to the selection of prognostic factors, which must support an effective therapeutic planning.