Estradiol 17 beta-hydroxysteroid dehydrogenase activity in human breast fibroadenomas

In the human endometrium, the presence of the progesterone-dependent enzyme 17 beta-hydroxysteroid dehydrogenase (E2DH) permits the conversion of an active estrogen, estradiol, into a less active one, estrone. This E2DH activity contributes to the antiestrogenic properties of progesterone. In the present study, E2DH activity was assayed in 54 surgically removed fibroadenomas. This benign breast disease was chosen since it offers rather homogeneous epithelial concentrations and still remains close to normal breast tissue from a pathological and hormonal point of view. E2DH activity was highest in fibroadenomas with high epithelial cell density. In addition, in these high epithelial cell density fibroadenomas (n = 18), E2DH activity increased markedly throughout the luteal phase of the menstrual cycle. Thus, it was 3- to 4-fold higher in fibroadenomas removed at the end of the luteal phase (1520 +/- 166 fmol/mg protein.h) than in those obtained during the follicular phase (375 +/- 95 fmol/mg protein.h). In addition, a striking increase in E2DH activity was observed in fibroadenomas from 5 patients treated with oral progestins (4080 +/- 650 fmol/mg protein.h) and 3 patients receiving progesterone topically applied upon the breast (3830 +/- 475 fmol/mg protein.h). E2DH activity, therefore, appears to be an important mechanism involved in the control by progesterone of estradiol action in breast tissue, as it is in the endometrium. It is also a good index of cellular differentiation and progesterone action at the molecular level. It is hypothesized that E2DH activity might be a specific marker of progesterone receptor itself and could be proposed in the evaluation of the hormone dependence of human breast tissue.