Estrogen-Induced Prolactinoma in a Man

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Abstract
Prolactinomas can be induced in rats by large doses of estrogens. Whether prolactinomas can be induced in humans by estrogens, however, is not known. This report describes the development of a prolactinoma in a man with previously normal plasma PRL levels after the administration of pharmacological doses of estrogen. The patient, a 26-yr-old male to female transsexual, took cyproterone acetate (100 mg/day, orally) and ethinyl estradiol (100 μg/day, orally) for 10 months and (surreptitiously) estradiol-17-undecanoate (100 mg, twice weekly, im) for about 6 of the 10 months. Plasma PRL levels rose from 0.05 to 5.20 U/L within 10 months (normal, 0.05–0.30 U/L). A computed tomographic scan showed a pituitary mass with suprasellar extension. After all estrogen therapy was discontinued, his plasma estradiol levels gradually declined from 2.8 to 0.77 nmol/L (normal, 0.04–0.12 nmol/L), but PRL levels rose further to 6.2 U/L. Bromocriptine treatment (2.5 mg twice daily) then was given. Plasma PRL fell gradually to 0.43 U/L and a computed tomographic scan after 5 months showed reduction in tumor size. The patient then discontinued bromocriptine treatment. Four months later his plasma estradiol level was normal, while plasma PRL had risen to 4.6 U/L, indicating autonomous PRL secretion. We conclude that 1) estrogen in pharmacological doses can induce prolactinomas in man; and 2) subjects treated with high doses of estrogen must, therefore, be surveyed for the development of such tumors.