Background: The treatment of bone metastasis in association with thyroid cancer represents a difficult challenge. Given the paucity of patients with bone metastasis and the difficulty of treating this disease, few studies have investigated the clinical features and prognostic factors of bone metastasis from differentiated thyroid cancer. Methods: During the 31-year-period from 1976 to 2006, a total of 1,398 patients underwent initial thyroidectomy at Cancer Institute Hospital for differentiated thyroid carcinomas, including standard papillary thyroid carcinoma, papillary microcarcinoma (primary tumor diameter ≤1.0 cm), and follicular thyroid carcinoma. Among these, 25 (2%) patients displayed bone metastasis at initial presentation (synchronous) and 27 patients showed bone metastasis during follow-up (metachronous). The records for these 52 patients were reviewed retrospectively to identify prognostic factors and analyze treatment strategies. Results: Univariate analysis for disease-specific survival indicated metachronous bone metastasis and the presence of distant metastasis at sites other than bone as indicators of significantly worse prognosis. The type of cancer (papillary thyroid carcinoma versus follicular thyroid carcinoma) was not a significant indicator of prognosis; however, patients with papillary microcarcinoma showed significantly worse survival than patients with standard papillary and follicular thyroid carcinoma. A significant survival advantage was observed among patients who underwent radioactive iodine therapy, and better prognosis seemed to be obtained with greater doses of radioactive iodine. Operative resection of metastatic bone lesions also seemed to be associated with better prognosis. A multivariate analysis for disease-specific survival identified the coexistence of distant metastasis at sites other than bone as the only independent variable indicative of poor prognosis. Conclusion: In the absence of definitive, effective treatments for this disease, radioactive iodine therapy combined with resection of bone metastasis, wherever possible, seems to represent the most potent therapy available. Although bone metastasis is a strong sign of poor prognosis, early detection and administration of appropriate therapy using radioactive iodine seems likely to improve the survival rate and quality of life in patients with bone metastasis from differentiated thyroid carcinoma.
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