Estrogens can become endogenous carcinogens via formation of catechol estrogen quinones, which react with DNA to form specific depurinating estrogen-DNA adducts. The mutations resulting from these adducts can lead to cell transformation and the initiation of breast cancer. Estrogen metabolites, conjugates and depurinating DNA adducts in urine samples from 46 healthy control women, 12 high-risk women and 17 women with breast cancer were analyzed. The estrogen metabolites, conjugates and depurinating DNA adducts were identified and quantified by using ultraperformance liquid chromatography/tandem mass spectrometry. The levels of the ratios of depurinating DNA adducts to their respective estrogen metabolites and conjugates were significantly higher in high-risk women (p < 0.001) and women with breast cancer (p < 0.001) than in control subjects. The high-risk and breast cancer groups were not significantly different (p = 0.62). After adjusting for patient characteristics, these ratios were still significantly associated with health status. Thus, the depurinating estrogen-DNA adducts are possible biomarkers for early detection of breast cancer risk and response to preventive treatment. (c) 2007 Wiley-Liss, Inc.