Amelioration of postmenopausal primary hyperparathyroidism during adjuvant tamoxifen for breast cancer.

The effects of adjuvant treatment with tamoxifen on bone metabolism in a postmenopausal woman with primary hyperparathyroidism is presented. A 69-year-old woman with increased serum ionized calcium, parathyroid hormone, and 1,25-(OH)2 vitamin D levels and a normal bone scan received tamoxifen 10 mg three times daily for 1 year. During treatment bone turnover decreased whereas parathyroid hormone increased further. After cessation of treatment the calcium metabolic variables returned to pretreatment levels. The antiestrogen tamoxifen seems to behave as an estrogen on bone metabolism in primary hyperparathyroidism.