Fig. 1. Local estrogen homeostasis in an estrogen-responsive cell. Unlike ovarian and breast tissue, the endometrium does not possess enzymes to transform DHEA into estrogens and it is generally acknowledged that aromatase expression and activity in the endometrium is restricted to women with endometrial diseases.97 2OHE2 = 2-hydroxyestradiol; 3β-HSD-2 = 3β-hydroxysteroid dehydrogenase type 2; 4OHE2 = 4-hydroxyestradiol; 2/4MeOE2 = 2-/4-methoxyestradiol; 17β-HSD = 17β-hydroxysteroid dehydrogenase; ADIONE = androstenedione; AhR = aryl hydrocarbon receptor; arnt = AhR nuclear transferase; COMT = catechol-O-ethyltransferase; CYP1A1 = cytochrome P450 1A1; CYP1B1 = cytochrome P450 1B1; DHEA = dehydroepiandosterone; DHEAS = dehydroepiandosterone sulfate; DRE = dioxin responsive element; E2 = estradiol; E1 = estrone; E1S = estrone-3-sulfate; E2S = estradiol-3-sulfate; ERE = estrogen responsive element; SULT = sulfotransferase; TESTO = testosterone.