Bone metastases from differentiated thyroid cancer: characteristics and prognostic factors in a multicenter series

Objective: The aim of this study is to describe the characteristics, survival and prognostic factors of a cohort of patients with bone metastases (BMs) from differentiated thyroid carcinoma (DTC).Methods: This was a multicenter retrospective observational study including patients diagnosed with BMs from DTC between 1980 and 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 the survival analysis and comparison between groups.Results: Sixty-three patients were evaluated. Median follow-up from BM diagnosis was 35 (15-68) months. About 30 (48.4%) patients presented with synchronous BMs. Regarding histology, 38 (60.3%) had the papillary variant. BMs 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 (hazard ratio (HR): 2.916; 95% confidence interval (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.