THYROID-FUNCTION TEST CHANGES WITH ADJUVANT TAMOXIFEN THERAPY IN POSTMENOPAUSAL WOMEN WITH BREAST-CANCER

Purpose: While tamoxifen has been shown to alter concentration of many hormones and their binding globulins, there have been conflicting res ults regarding its effects on thyroid function tests. We sought to cla rify these effects by studying subjects in a controlled clinical trial . Patients and Methods: We evaluated a subset of postmenopausal women who had participated in a longitudinal, double-blind, randomized, plac ebo-controlled toxicity study of tamoxifen 10 mg orally, twice daily. There were 14 subjects in both the tamoxifen and placebo groups. Measu rement of thyroid-binding globulin (TBG), thyroxine uptake (T-Uptake), thyroxine (T-4), and thyroid-stimulating hormone (TSH), and an indire ct estimate of the free T-4 index (FTI), were made for each subject be fore and after 3 months of treatment. Results: For T-Uptake, T-4, and TBG, there were significant increases in the mean change from baseline to 3 months in the tamoxifen group compared with the placebo group (P = .02, .0001, and .003, respectively), while there were no significan t changes in the measured TSH and in the calculated FTI. Conclusion: W e conclude that tamoxifen therapy in postmenopausal women results in i ncreased TBG, with secondary increases in measured T-Uptake and T-4 fo llowing. However, TSH and FTI levels are unchanged, and treated women remain eumetabolic. J Clin Oncol 13:854-857. (C) 1995 by American Soci ety of Clinical Oncology.