Improved Survival After Multimodal Approach with 131I Treatment in Patients with Bone Metastases Secondary to Differentiated Thyroid Cancer.

Background: The objective of this study was to evaluate the overall survival (OS) of radioiodine (131I) treatments alone or combined with non-131I treatments in patients with bone metastases (BM) of differentiated thyroid cancer (DTC). Methods: This was a retrospective study of patients who were evaluated between 2001 and 2018 at MedStar Washington Hospital Center and who had DTC, BM, and at least one 131I treatment after the diagnosis of BM. The OS was analyzed by Kaplan-Meier survival curves and was compared by log-rank test between two groups: patients who received 131I treatments alone and those who received treatments combining 131I with non-131I treatments (CombTx). Non-131I treatments include surgery, radiofrequency ablation, cryotherapy, arterial embolization, external beam radiation, Cyberknife, systemic targeted therapy, and anti-resorptive medication. Results: A total of 77 patients met the above criteria and were followed up to 41 years. Thirty percent (23/77) of patients received 131I treatment alone, and 70% (54/77) received CombTx. For 131I treatment alone, the median survival was 3.9 years, and the 1-, 2-, 3-, 5-, and 10-year OS rates were 86%, 81%, 61%, 35%, and 23%, respectively. For CombTx, the median survival was 7.7 years, and the 1-, 2-, 3-, 5-, and 10-year OS rates were 96%, 92%, 86%, 69%, and 30%, respectively. Patients who had undergone initial 131I therapy within six months post thyroidectomy demonstrated a better median survival after BM diagnosis than those whose initial 131I therapy was six months or more after thyroidectomy (6.5 vs. 0.5 years; p < 0.001). Patients who received external beam radiation therapy demonstrated a better median survival than those who did not (7.8 vs. 4.4 years; p = 0.016). Patients who received denosumab demonstrated a better median survival than those who did not (7.7 vs. 5.2 years; p = 0.03). Patients who were <55 years of age at the initial diagnosis of DTC or at the initial diagnosis of BM had a better median OS than those diagnosed at ≥55 years of age (both p = 0.01). In the multivariate analysis, only age at initial diagnosis of DTC and initial 131I therapy within six months post thyroidectomy, and multiple 131I treatments were independent prognostic factors. Conclusions: In patients with DTC with BM, 131I treatment in combination with one or more non-131I direct and systemic treatments was associated with a significant increase in OS compared with those patients who were treated by 131I treatment alone.