ObjectiveTo determine the levels of free estrone (E1) and estradiol (E2) in breast adipocytes of premenopausal women, premenopausal women using oral contraceptives (OCs), postmenopausal women, and postmenopausal women using estrogen replacement therapy (ERT).MethodsBreast adipose tissue was obtained from 36 premenopausal and 29 postmenopausal women, and adipocytes were separated from stromal and epithelial cells through collagenase digestion and centrifugation. Oil was rendered from adipocytes, and E1 and E2 levels were measured by specific radioimmunoassays after extraction with methanol-water.ResultsEstrone and E2 levels were approximately 2.4- and 7.8-fold higher, respectively, in premenopausal women than in postmenopausal women. In premenopausal women, E1 and E2 correlated with the time since last menses (R2= .55 and .62, respectively), whereas in postmenopausal women, E1 and E2 correlated with body mass index (BMI) (r= .48 and .52, respectively). Estrone levels were always greater than E2 levels in adipocytes, with the E1/E2 ratio being 2.7-fold higher in postmenopausal women than in premenopausal women. The use of OCs decreased E1 and E2 levels in premenopausal women, and ERT increased levels in postmenopausal women.ConclusionFree estrogen in breast adipocytes is characterized by E1 dominance, with levels in premenopausal women correlating with the menstrual cycle and levels in postmenopausal women correlating with BMI.