Metabolism of [ 3H]oestradiol in vivo by normal breast and tumour tissue in postmenopausal women

Tumour and normal breast tissue was obtained from postmenopausal breast cancer patients following [ 3H] oestradiol infusion (50 μCi over a 12 h period). The fraction of radioactivity present as oestradiol or oestrone was measured and the results expressed both as the ratio of oestradiol-oestrone and as the percentage oestrogen present as oestrone, and the findings compared with in vitro measurements of 17β-hydroxysteroid dehydrogenase activity. Concentrations of 5-androstene-3β,17β-diol, dehydroepiandrosterone and its sulphate and testosterone were measured and related to oestradiol metabolism. The study demonstrated that tumour tissue is less able to metabolise oestradiol to oestrone than is normal breast tissue and indicated that the ability of the tissue to detoxify oestradiol may be dependent on cofactor availability. The results also supported the possibility that increased tissue concentrations of adrenal androgens inhibit oestradiol and thus increase tissue exposure to oestradiol.