Abstract
Background: Bone is the second most frequent target of distant metastases in patients with differentiated thyroid cancer (DTC). However, there is a controversy regarding the longterm outcome of the breast cancer patients wtih bone metastases. This study therefore was designed with the objective of assessing the clinical characteristics related to the long-term outcome and prognosis of patients with bone metastases. Methods: We reviewed the medical records of 360 patients of differentiated thyroid cancer followed at our institute from 2007 to 2012. A total of 57 patients were found to have bone metastases, who we analyzed with regard to their basic demographic data, clinical characteristics, treatment and clinical outcomes. Results: The incidence of bone metastases from thyroid carcinoma was 15.8%. The mean age at the diagnosis of bone metastases was 47±18 years (range 16 to 80 years); 46% patients were below 40 years of age and 53.8% of the patients were above 40 years of age. 15.3% were males and 84.6% were females. Histopathologic subtypes included papillary (38%), and follicular (45.6%). Multiple bone sites were involved in 50% of the patients with 29% of the patients with single bone site involvement; and 20.8% of the patients had metastases to other body organs. All patients underwent near-total thyroidectomy followed by aggressive radioiodine therapy. Number of 131I doses received ranged from 3 to 12 with a mean of 6.6. Mean dose of 131I per patient was 48914 MBq ± 20424 (Range: 18130 - 76960). Baseline thyroglobulin (TG) level ranged from 380ng/ml to 17300ng/ml with a mean value of 2250±5644 ng/ml. 60% of the patients showed a declining trend in TG over time, whilst 23% of the patients showed a rising trend; 6.2% of the patients had normal TG/ATG (antithyroglobulin) values throughout the course of disease. 10.4% of the patients had static TG levels. 64% of the patients with bone metastases showed 5-year survival. Conclusion: Multiple bone metastases represent a frequent complication of DTC especially of follicular thyroid cancer. In our population it is more common in females and in patients above 40 years of age. Overall survival rate is very good in the patients with bone metastasis if they are managed aggressively with total thyroidectomy and repeated radioactive iodine.

Key words: Differentiated thyroid cancer, Bone metastases, Radioiodine treatment