Intratumoral levels of estrogens in breast cancer.

Breast cancer tissue is an endocrine organ and particularly the estrogen biosynthetic properties of this tissue have been well studied. The concentration of estradiol in breast cancer tissue from postmenopausal patients is considerably higher than that in the circulation and appears to depend largely 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 estrogens (Cancer Res. 53: 4563, 1993) as well as intratumour aromatase, median aromatase activity being 89% lower in the tissue from patients pretreated with aromatase inhibitor 7 days prior to surgery (P < 0.001). Also the intratissue concentrations of estrogens were decreased (64% and 80% reduction, respectively for estrone and estradiol; P = 0.001 and <0.05; Cancer Res. 57: 2109, 1997). These results illustrate that intratissue estrogen biosynthesis is effectively inhibited by the new generation of aromatase inhibitors. The pathophysiological consequences of this finding are currently under study.