Estrogenic action of tamoxifen in women treated with luteinizing hormone-releasing hormone agonists (goserelin)--lack of shrinkage of uterine fibroids.

Six premenopausal women with uterine fibroids were treated with a combination of tamoxifen, 20 mg/d, and goserelin, 3.6 mg every 28 days, for a total of 24 weeks. Results were compared with those from six women, matched for pretreatment uterine volume, who had been treated with goserelin alone. During combined therapy, plasma and urinary estrogen concentrations were significantly lower than during goserelin alone, whereas sex hormone binding globulin concentrations were significantly higher. Plasma luteinizing hormone and follicle stimulating hormone (FSH) concentrations were both suppressed, in contrast with results during goserelin alone when FSH levels remained within the pretreatment range. None of the women on combined therapy bled in response to the endocrine changes of the initial treatment cycle. Despite this profound pituitary-ovarian suppression, there was no significant change in uterine volume during combined therapy. These results suggest that tamoxifen is acting as an estrogen agonist in women rendered hypoestrogenic with luteinizing hormone-releasing hormone agonists.