Improved survival after multimodal approach with 131I treatment in patients with bone metastasis secondary to differentiated thyroid cancer.

BACKGROUND: The objective of this study was to evaluate the overall survival (OS) of 131I treatments alone and when combined with non-131I treatments in patients with bone metastases (BM) secondary to differentiated thyroid cancer (DTC).

METHODS: This was a retrospective study of patients who were evaluated between 2001-2018 at MedStar Washington Hospital Center and had differentiated thyroid cancer (DTC), bone metastases (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 combined 131I treatments with non-131I treatments (CombTx).

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 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 were 96%, 92%, 86%, 69%, and 30%, respectively. Patients who had undergone initial 131I therapy within six months post-thyroidectomy (6.5 vs. 0.5 years; P<0.001), external beam radiation therapy (7.8 vs. 4.4; p=0.016) or received denosumab (7.7 vs. 5.2 years; p=0.03) demonstrated a better median survival than those who did not. Patient who were age <55 years at the initial diagnosis of DTC or at the initial diagnosis of BM had a better median OS than those diagnosed at age ≥55 (both p=0.01). In the multivariate analysis, only age at initial diagnosis of DTC and initial 131I therapy within six months post-thyroidectomy were independent prognostic factors.

CONCLUSIONS: In patients with differentiated thyroid cancer with bony metastases, 131I treatment in combination with one or more non-131I direct and systemic treatments had a significant increase in overall survival compared with those patients who were treated by 131I treatment alone.