Long-Term Adjuvant Therapy with Tamoxifen: Effects on Sex Hormone Binding Globulin and Antithrombin III

Plasma levels of luteinizing hormone, sex hormone binding globulin, and antithrombin III were measured in pre-and postmenopausal breast cancer patients receiving adjuvant combination chemotherapy or combination chemotherapy and long-term tamoxifen therapy. The aim was to determine the estrogen-like effects of tamoxifen. The premenopausal patients had received tamoxifen for between 434 and 2592 days and postmenopausal patients between 91 and 1560 days. Tamoxifen caused a consistent rise in sex hormone binding globulin in premenopausal (P < 0.03) and postmenopausal (P < 0.01) patients compared to chemotherapy controls. Luteinizing hormone levels were only significantly lowered (P < 0.008) in premenopausal patients compared to chemotherapy controls. Antithrombin III levels were significantly depressed (P < 0.001) in postmenopausal patients compared with chemotherapy controls. However, none of the patients had a value that was depressed by more than 30% of the laboratory control (the level of clinical significance). The mean for the group was 90% ± 4 (mean ± SD, N = 11). The estrogen-like rise in sex hormone binding globulin produced by adjuvant tamoxifen therapy could be advantageous for maintaining the antiestrogenic action of the drug. A decrease in antithrombin III occurred but was not within a range of clinical concern. We recommend, however, that patients with a history of thromboembolic disorders should be monitored carefully if placed on tamoxifen therapy.