Many of the causes of breast cancer are known, but many are not. One established risk factor is alcohol consumption. In fact, it is the best documented risk factor (other than familial and hormonal risk factors such as number of pregnancies and age at menopause. The reasons why alcohol drinking causes breast cancer have not been well studied. This is an important issue because many women make lifestyle choices about drinking, and there is data that moderate drinking prevents heart disease. Also, alcohol drinking can adversely interact with hormone replacement therapy to increase breast cancer risk further. It also is important to study alcohol drinking because many of the reasons why it causes breast cancer are the same for other risk factors, such as the diet. We will study four ways that alcohol drinking can cause breast cancer. Our hypotheses are that breast cancer risk is increased with drinking because: (1) It affects estrogens in the body and a woman's responses to estrogens; (2) it increases oxidative stress and damage to DNA and proteins; (3) it causes mutations via metabolites of alcohol; and (4) it interacts with dietary folic acid to affect gene regulation and mutations. Further, we hypothesize that each of these mechanisms are affected by genetic traits, as well as diet. It is expected that some of the mechanisms will play greater roles than others. Definitive conclusions will come from examining the evidence from complementary and corroborative study designs. We will study the effects of drinking, diet, and genetic polymorphisms involving the above hypothesized pathways. The aims of the Center are: (1) To use a previously conducted breast cancer case-control study of 1,131 cases and 2,021 controls that will allow us to directly examine breast cancer risk; (2) to conduct a study of mammographic breast density in 1,064 Caucasian and African American women considering breast density as an intermediate biomarker of breast cancer risk; (3) to conduct an intensive biomarker study of the tissues from 100 Caucasian and African American cancer-free women undergoing reduction mammoplasty, which will provide insights into early carcinogenic changes; and (4) to utilize several different experimental animal models that will provide mechanistic data that can be corroborated across studies. The Center will utilize a multidisciplinary approach that can answer questions in an integrated fashion by four institutions. Our research strategy bridges basic to population science. Among the different, but corroborative study designs listed above, we will investigate the same hypotheses using mostly the same biomarkers and study instruments, all in relation to alcohol drinking. We will study cancer patients, women who never had cancer, and several animal models. The human studies contain virtually the same questionnaires, and the animal studies mimic human alcohol and dietary exposures. The studies share both well-established and novel biomarkers, such as gene hypermethylation, mitochondrial mutations, microarrays, p53 mutations, comparative genomic hybridization, protein analysis for adducts and metabolizing genes, DNA adducts for oxidative damage, estrogen receptor analysis, markers of proliferation digital mammography, and MRI of mammary glands. The same genetic traits will be examined in all the human studies. Alcohol drinking causes about 17,000 new breast cancer cases per year. While seemingly low (although it is not), this is the major known modifiable risk factor and affects about four times more women than those from high risk families. Just as we can learn a lot about women's risk in general by studying women from high risk families, the same also is true for the study of alcohol drinking, because it is a paradigm for other risk factors. Definitive studies on breast carcinogenesis would lead to improved public health recommendations, allow for women to make individual choices about lifestyle and risk, place alcohol drinking into a broader context of interactions with other choices such diet, hormone replacement therapy, etc., and lead to more rationale prevention strategies.