Although European-American (EA) women, overall, have higher incidence of breast cancer than African-American (AA) women, AA women are more likely to be diagnosed at a younger age, and to have more aggressive tumors, characterized by higher grade, higher proliferative indices, and lack of expression of estrogen and progesterone receptors. The reasons for these racial differences in breast cancer biology and age at onset are unknown, but it is possible that differential gene methylation could affect these differences in tumor biology. Furthermore, little is known regarding factors that affect gene methylation in breast cancer. Insight into predictors of gene methylation could target risk factors for aggressive breast cancer in both AA and EA women for prevention. To investigate this question, we will perform a two stage design study. In the first discovery stage, we will perform genome-wide methylation on a sample of 100 freshly frozen tissues from 100 AA and 100 EA breast cancer patients for discovery of genes that are most differentially methylated between the races and that differentiate between high and low aggressive disease. Those most significantly different by race and aggressiveness will be assessed in tissues from women participating in an on-going case-control study designed to investigate predictors of early/aggressive breast cancer in AA women. Using the Illumina GoldenGate Assay, tissues from 500 AA and 500 EA women will be evaluated to determine if methylation patterns differ between the groups. We will also determine if methylation is associated with younger age, ER status and ''triple negative' tumors. Finally, we will investigate the potential role of folate and related nutritional factors, as well as alcohol consumption in predicting methylation patterns within each group. Results from this study will provide extremely important information regarding the etiology of aggressive breast cancers, and may greatly elucidate reasons for this more lethal form of disease among AA women. Because methylation can be reversed, interrogation of these differences could identify targets for prevention and early detection, as well as for treatment.