Intratumoral levels of estrogens in breast cancer

Breast cancer tissue is an endocrine organ and particularly the estrogen bi osynthetic properties of this tissue have been well studied. The concentrat ion of estradiol in breast cancer tissue from postmenopausal patients is co nsiderably higher than that in the circulation and appears to depend largel y on local production. Androgenic precursor steroids are abundantly present , but estrogen storage pools like fatty acid derivatives appear to be less important than initially thought. New, potent and highly specific aromatase inhibitors effectively inhibit peripheral conversion of androgens to estro gens (Cancer Res. 53. 4563, 1993) as well as intratumour aromatase, median aromatase activity being 89% lower in the tissue from patients pretreated w ith aromatase inhibitor 7 days prior to surgery (P < 0.001). Also the intra tissue concentrations of estrogens were decreased (64% and 80% reduction, r espectively for estrone and estradiol; P = 0.001 and <0.05; Cancer Res. 57: 2109, 1997). These results illustrate that intratissue estrogen biosynthes is is effectively inhibited by the new generation of aromatase inhibitors. The pathophysiological consequences of this finding are currently under stu dy. (C) 1999 Elsevier Science Ltd. All rights reserved.