Cancer is considered to be a genetic disease in the sense that it is triggered by mutations. In general, scientists have thought that estrogens increase the rate of cell division, leading to more mutations during DNA replication. Recent scientific findings support the idea that the reaction of certain metabolites of natural estrogens with DNA can lead to the mutations that induce breast cancer. The hypothesis that DNA-damaging estrogen metabolites initiate breast cancer is at the center of the research proposed in this Breast Cancer Center of Excellence. Furthermore, by preventing this damage to DNA, one could expect to inhibit the processes leading to breast cancer. A team of experienced scientists has interacted for the past 6 years in a National Cancer Institute-sponsored focus group called the Cancer Cube (C3, Complementary x Collaborative x Coalition). They have assembled to study the DNA-damaging role of estrogen metabolites in human breast cancer. The Center of Excellence will be composed of leading scientists from the University of Nebraska Medical Center, Omaha, Nebraska (E. Cavalieri and E. Rogan), Mayo Clinic, Rochester, Minnesota (J. Ingle), Stehlin Foundation for Cancer Research, Houston, Texas (J. Liehr), Fox Chase Cancer Center, Philadelphia, Pennsylvania (J. Russo), University of Virginia Health System, Charlottesville, Virginia (R. Santen), and University of Memphis, Memphis, Tennessee (T. Sutter). The proposed research will include testing the ability of two different preventing agents to inhibit the development of mammary tumors in female rats treated with the natural estrogen estradiol. To elucidate the processes involved in forming estrogen metabolites, at selected time points, rats from the various test groups will be sacrificed and the profile of estrogen compounds in the mammary tissue of the rats will be determined. In addition, the levels of selected estrogen-metabolizing enzymes will be analyzed. The effects of estrogen metabolites on the processes involved in changing normal human breast cells to cancer cells will be studied in cell culture. The ability of the preventing agents to block these changes, and the profiles of estrogen compounds in the treated cells will also be determined. Prevention of estrogen-induced mutations in genes relevant to cancer will be studied in the same cells. The role of estrogens in causing breast cancer is thought to be dependent on high levels of estrogens being produced in regions of the breast rather than coming from circulating estrogens. To study this, the profile of estrogen compounds in mouse mammary tissue will be determined and the ability of the anticancer drug letrozole to inhibit formation of tumors will also be investigated. In addition, the role of estrogens in the induction of mammary tumors in mice will be studied in female mice that do not have estrogen receptors. A study of the profile of estrogen compounds in human breast fluid collected by a procedure called ductal lavage will be conducted to determine whether analysis of this fluid might be developed into a noninvasive bioassay for risk of developing breast cancer. The results of the mammary tumor prevention studies in animals and the inhibition of mutations and changes in cultured human breast cells leading to cancer will be used to design and prepare a clinical trial of breast cancer prevention in women. The studies proposed in this Center will be conducted in a highly collaborative manner, with scientists at several institutions contributing to each study. Consumer advocates will be involved in maximizing the research so that it has major implications for preventing and diagnosing human breast cancer. They will prepare a lay overview of the research and a layman¿s guide to the scientific terminology used in basic cancer research and will disseminate the findings to the public in collaboration with a number of breast cancer advocacy groups. The results from this Center are expected to provide highly promising strategies for preventing human breast cancer and for determining a woman¿s risk of developing this disease.