Breast cancer is a tragedy affecting nearly 180,000 newly diagnosed women and killing more than 43,000 each year. One of the requirements for progress in understanding the etiology and improving the treatment of this disease is the development of new animal models in which normal mammary gland biology and all stages of carcinogenesis can be investigated. The tools are in place to prepare new mouse models for mammary gland research; what is needed is a dialog between basic and clinical researchers about the molecular and tumor biology of human cancer initiation and progression and their correlates and approaches to modeling in mice. The Jackson Laboratory is establishing a series of meetings on mouse models for human cancers with the overall goal of discussing the development and validation of accurate preclinical mouse models and their use in translational cancer research. The first meeting, (October 5-8, 1999) will focus on mammary carcinogenesis with the specific objectives of: l) evaluating current approaches to modeling aspects of human mammary cancer in mice; 2) delineating current hypotheses regarding oncogenesis in the mammary gland; 3) communicating recent advances in understanding and modeling processes of angiogenesis and metastasis; 4) comparing and contrasting the hormonal control of mammary epithelium in human and mouse; 5) discussing novel therapeutic and preventative strategies and mouse models needed to test them; 6) providing experience in interpreting and comparing histopathology in mouse and human; 7) discussing informational and other resources needed by the community; and 8) preparing an online proceedings of the meeting.