Intratumoral activity of the progesterone-dependent enzyme 17β-hydroxysteroid dehydrogenase (E2DH) was measured in 114 patients with breast cancer (33 pre- and 81 postmenopausal) before and/or after 8 days of a progestin treatment (lynestrenol, 10 mg/day). In 12 postmenopausal patients, the ability of E2DH to be stimulated by lynestrenol was compared to estradiol receptor (ER) and progesterone receptor (PR) levels.

In premenopausal patients, E2DH was higher when tumors were excised in the luteal phase than when excised in the follicular phase. In postmenopausal patients, E2DH was higher after progestin treatment. However, E2DH stimulation by lynestrenol depended on receptor levels. It was most often markedly stimulated in ER-positive, PR-positive tumors. It remained low in ER-negative, PR-negative tumors.

Intratumoral measurement of the progesterone-dependent enzyme E2DH in breast cancer after progestin treatment could therefore provide a fine and reliable index of the presence and functional character of PR and hormone dependency of the tumor.

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