Involvement of up-regulation of 17 beta-hydroxysteroid dehydrogenase type 1 in maintenance of intratumoral high estradiol levels in postmenopausal breast cancers

Estradiol (E2) and estrone (E1) levels as well as mRNA expression levels of aromatase, sulfatase and 17 beta -hydroxysteroid dehydrogenase type 1 (17 beta -HSDI) in breast cancer tissues were studied to elucidate the mechanis m involved in the maintenance of the intratumoral high E2 levels in postmen opausal patients with very low serum E2 levels. Intratumoral E2 levels of p ostmenopausal patients (127.2 +/- 17.5 pg/g) (mean +/- SE) were not signifi cantly different from those of premenopausal patients (110.1 +/- 10.1 pg/g) (p=0.36). The mRNA expression levels of aromatase and sulfatase, determine d by a quantitative real-time PCR, were not significantly different between premenopausal and postmenopausal breast cancers, but 17 beta -HSDI mRNA ex pression levels were significantly higher in postmenopausal than premenopau sal breast cancers (p<0.05). Intratumoral E2/E1 ratios were significantly h igher in postmenopausal than premenopausal breast cancers (p<0.01). These r esults demonstrate that the increased conversion from E1 to E2 catalyzed by 17 beta -HSDI may play an important role in the maintenance of the intratu moral high E2 levels in postmenopausal patients. (C) 2001 Wiley-Liss. Inc.