Specific Aims The Cooperative Breast Cancer Tissue Resource (CBCTR) was developed, starting in 1993, in response to a cooperative agreement between the National Cancer Institute and four sites in the United States to provide breast cancer tissue to the biomedical research community for the study of clinical markers of tumor prognosis and the evaluation of promising diagnostic tests based on these markers. The current application is a response to a Letter Request for Applications for Recompetition of the CBCTR for a further three years of funding. Specifically, these four institutions individually and together will 1. Continue the provision of specimens to researchers in the community from the files of the CBCTR. The material provided will be mainly in the form of Tissue Microarrays that incorporate specimens from hundreds of cases on one or two slides. The CBCTR will, however, retain the ability to fill requests for sections of breast cancer material from a number of individual cases when the particular experiment can only be done with such material. 2. Continue the collection and updating of clinical and outcome data on each site's cases to assure the most accurate and contemporary material for each case. Such review will exploit automated sources of data but will also likely require review of a considerable number of primary sources: the medical records of these women. 3. Replenish the CBCTR for the cases that have been used by researchers. The CBCTR is currently a finite resource and is not being replenished with the addition of new cases. It has been designed to be used and, inevitably, depleted by its client cancer researchers. On the other hand, if funding becomes available and the National Cancer Institute decides to maintain a large and representative mixture of breast cancers in the CBCTR, each site can replenish the Resource by accrual of new cases diagnosed since 1993, when the original application was funded and after which few new cases were accrued.