Skeletal Complications and Mortality in Thyroid Cancer: A Population-Based Study

Abstract

Abstract Context: Although bone is a common site for tumor metastases, the burden of bone events [bone metastases and skeletal-related events (SREs)] in patients with thyroid cancer is not well known. Objective: To measure the prevalence of bone events and their impact on mortality in patients with thyroid cancer. Patients, Design, and Setting: We identified patients diagnosed with thyroid cancer between 1991 and 2011 from the linked Surveillance Epidemiology and End Results–Medicare dataset. Multivariable logistic regression was used to identify the risk factors for bone metastases and SREs. We used Cox proportional hazards regressions to assess the impact of these events on mortality, after adjusting for patient and tumor characteristics. Results: Of the 30,063 patients with thyroid cancer, 1173 (3.9%) developed bone metastases and 1661 patients (5.5%) developed an SRE. Compared with papillary thyroid cancer, the likelihood of developing bone metastases or an SRE was higher in follicular thyroid cancer [odds ratio (OR), 2.25; 95% confidence interval (CI), 1.85 to 2.74 and OR, 1.40; 95% CI, 1.15 to 1.68, respectively] and medullary thyroid cancer (OR, 2.16; 95% CI, 1.60 to 2.86 and OR, 1.62; 95% CI, 1.23 to 2.11, respectively). The occurrence of a bone event was associated with greater risk of overall and disease-specific mortality [hazard ratio (HR), 2.14; 95% CI, 1.94 to 2.36 and HR, 1.59; 95% CI, 1.48 to 1.71, respectively]. Bone events were a poor prognostic indicator even when compared with patients with other distant metastases (P < 0.001 and P < 0.001 for overall and disease-specific mortality, respectively). Conclusions: Bone events in patients with thyroid cancer are a poor prognostic indicator. Patients with follicular and medullary thyroid cancers are at especially high risk for skeletal complications.