Long-Term Outcomes and Prognostic Factors in Patients With Differentiated Thyroid Carcinoma and Bone Metastases

Objective: This institutional study sought to retrospectively evaluate disease progression and survival of patients with differentiated thyroid cancer (DTC) and bone metastases (BM) and to investigate variables predictive of better long-term outcomes.Methods: The Rabin Medical Center Thyroid Cancer Registry was searched for patients with bone-metastatic DTC. Variables including a patient's gender and age, pathology of the thyroid tumor, and characteristics of BM were retrieved and analyzed in association with disease progression and mortality.Results: The cohort included 64 patients (48.4% female). Mean age at diagnosis was 62.1 ± 14.3 years; mean primary tumor size was 41 ± 30 mm. Overall, 60.4% had stage T3/T4 disease; 46.3% had extrathyroidal extension; 40% had lymph-node metastases. Histopathology yielded papillary and follicular DTC in 40.6% and 32.8% of patients, respectively, and poorly/intermediately differentiated carcinoma in 26.6%. BM were synchronous in 50%. Mean follow-up was 11 ± 9.6 years from DTC detection. The common first sites of BM detection were spine (46.9% of patients), pelvis (37.5%) and ribs (21.9%). Nineteen patients (29.7%) presented with multiple-site BM, of whom 15 (78.9%) had spinal metastases. After initial treatment, 62/64 patients had structural persistence, and at last follow-up, 57.8% had progressive disease. Overall, 54.7% of patients died, 71.4% of DTC. Improved long-term outcomes were associated with younger age, lower tumor stage, no extrathyroidal extension, bone-only metastases, and non-spinal BM. Younger age and non-spinal BM were the only independent predictors for improved survival.Conclusions: Selected patients with bone-metastatic DTC may achieve fair long-term outcomes. Spinal metastases are associated with disseminated skeletal spread and increased mortality.Abbreviations: BM = bone metastases; COX = multivariate analyses; DM = distant metastases; DSM = disease-specific mortality; DSS = disease-specific survival; DTC = differentiated thyroid carcinoma; ETE = extrathyroidal extension; LNM = lymph node metastases; OM = overall mortality; OS = overall survival; PTCFV = papillary thyroid carcinoma; RAI = radioactive iodine; SM = spinal metastases; SRE = skeletal-related event; txWBS = whole-body scan after RAI therapy