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Objective: To describe the characteristics, survival and prognostic factors of a cohort of patients with bone metastases (BM) from differentiated thyroid carcinoma (DTC). Methods: This was a multicenter retrospective observational study including patients diagnosed with BM from DTC between 1980-2021. A Cox-regression was performed to study prognostic factors for 5- and 10-year survival. Kaplan-Meier and log-rank tests were performed for survival analysis and comparison between groups. Results: Sixty-three patients were evaluated. Median follow-up from BM diagnosis was 35(15-68) months. 30(48.4%) patients presented with synchronous BM. Regarding histology, 38(60.3%) had the papillary variant. BM were multiple in 32(50.8%) patients. The most frequent location was the spine (60.3%). Other metastases were present in 77.8%, mainly pulmonary (69.8%). Concerning treatment, 54(85.9%) patients received I131, with BM uptake in 31(49.2%), and 25(39.7%) received treatment with multikinase inhibitors. Regarding complications, 34(54%) patients had skeletal-related events, 34(54%) died and 5- and 10-year overall survival was 42.4% and 20.4%, respectively. Significant prognostic factors in the multivariate analysis were the presence of lymph node involvement (HR 2.916 (95% CI 1.013-8.391);p=0.047) and treatment with I131 (HR 0.214 (95% CI 0.069-0.665);p=0.008) at 5 years, the presence of other metastases (HR 6.844. 95% CI 1.017-46.05;p=0.048) and treatment with I131 (HR 0.23 (95% CI 0.058-0.913);p=0.037) at 10 years. Conclusions: Our study reflects the management of patients with bone metastases from differentiated thyroid carcinoma in real clinical practice in several centers in southern Spain. Overall survival at 5 and 10 years was lower in patients who were not treated with I131, had nodal involvement and/or had other metastases.

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