Purpose: The objectives of this study were to prospectively delineate the efficacy and safety of zoledronic acid for treating bone metastases (BM) from differentiated thyroid carcinoma (DTC), and to evaluate the relationships between levels of bone metabolic markers and occurrence of skeletal-related events (SREs). Methods: This was a prospective, single-arm, single-center study. Nineteen patients with BM from DTC were assigned to receive zoledronic acid therapy every 4–5 weeks. Imaging studies for sites of BM were conducted every 6 months, and levels of bone metabolic markers, including serum bone-specific alkaline phosphatase (BAP) and urinary N-telopeptide of type I collagen (NTx), were assessed every 3 months. To evaluate the efficacy of zoledronic acid use, data of SREs were compared with those of 16 historical controls. Results: SREs developed in eight patients (42 %), but metastatic spinal cord compression (MSCC) appeared in only one patient. Pain scores were ameliorated in five patients, but aggravated in six patients. Ten patients had stable disease, six showed progressive disease, and none showed partial or complete response during the observation period. Decreases in levels of bone metabolic markers were observed in ten patients for BAP and 15 for NTx. However, no significant correlations were identified between changes in bone metabolic marker levels and development of SREs. Conclusions: Zoledronic acid may offer a mainstay of multidisciplinary treatment for patients with BM for the purpose of reducing SREs. Levels of serum BAP and urinary NTx do not appear reliable as indicators of amelioration of BM symptoms.
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