Abstract
To determine whether modulation of insulin-like growth factor-1 and insulin-like growth factor-binding protein-1 expression underlies the uterotropic effects associated with tamoxifen therapy in postmenopausal breast cancer patients. Using immunohistochemical techniques, we analyzed 37 endometrial specimens from biopsies (n = 18) or hysterectomies (n = 19) for Ki-67, insulin-like growth factor-1, and insulin-like growth factor-binding protein-1 expression. Specifically, five secretory- and three prolif erativephase endometrial specimens were used as controls; 20 specimens (including two endometrial adenocarcinomas) were analyzed from postmenopausal breast cancer patients treated with tamoxifen (20 mg/day) for at least 6 months; and nine endometrial adenocarcinoma specimens from patients not treated with tamoxifen were studied. Intensity of immunostaining was quantified using digitized imaging techniques. Insulin-like growth factor-1 and insulin-like growth factor-1-binding protein-1 were found to be expressed in normal and neoplastic endometrium of all patients, regardless of tamoxifen treatment. However, insulinlike growth factor-1 expression varied cyclically in histologically normal endometrium, was reduced in undifferentiated endometrial tumors, and was upregulated in tamoxifen-treated specimens. Insulin-like growth factorbinding protein-1 immunostaining did not vary during the menstrual cycle, but it was reduced significantly in benign tamoxifen-exposed tissue and endometrial adenocarcinomas, regardless of degree of differentiation or tamoxifen exposure. No correlation was found between the expression of insulin-like growth factor-1 and insulin-like growth factor-binding protein-1 and the proliferative indices of the tissues examined. The expression of insulin-like growth factor-1 and insulin-like growth factor-binding protein-1 in the uterus supports an automne and/or paracrine role for these proteins in endometrial physiology. Although further studies are needed, our investigation suggests that altered expression of insulin-like growth factor-1 and insulin-like growth factor-binding protein-1 may contribute to the uterotropic effects of tamoxifen. Funding for the study was provided by the Department of Clinical Investigation, Walter Reed Army Medical Center, and the Research Administration, Uniformed Services University of the Health Sciences.

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