LAUSR

OBJECTIVES In this study, we analyzed the effects of histology subtypes, lymph node N-stages, and the presence of extrathyroidal extensions on cancer-specific survival (CSS) and overall survival (OS) in patients with differentiated thyroid cancer. MATERIALS AND METHODS Cox proportional hazards regression analyses were carried out to evaluate the correlations between clinicopathological factors and CSS/OS. The combined effects of these factors on CSS and OS were then analyzed to determine the relative excess risk, attributable proportion, and synergy index. Kaplan-Meier curves were used to evaluate the mortality rate. RESULTS A total of 86033 cases were included in the analysis. Histology subtype, N-stage, and extrathyroidal extension were all found to be risk factors for CSS (hazard ratio [HR] = 1.8, 95% confidence intervals [CI]: 1.4-2.3, p < 0.001; HR = 1.9, 95% CI: 1.6-2.3, p < 0.001; HR = 1.4, 95% CI: 1.0-1.9, p = 0.035, respectively). The risk factors for OS were histology subtype and N-stage (HR = 1.3, 95% CI; 1.2-1.5, p < 0.001; HR = 1. 4, 95% CI: 1.3-1.5, p < 0.001, respectively) but not extrathyroidal extension (HR = 1.1, 95% CI: 0.9-1.3, p = 0.228). Furthermore, histology subtype and N-stage, histology subtype and extrathyroidal extension, and N stage and extrathyroidal extension (relative excess risk, attributable proportion, and synergy index: 48.8, 0.9, 7.6; 50.2, 0.7, 3.9; 7.0, 0.3, 1.6; respectively) were found to have significant synergistic effects. CONCLUSION Patients with follicular thyroid carcinoma (FTC) and extrathyroidal extension or lymph node metastasis are at a higher risk of mortality. Histology subtype, N-stage, and extrathyroidal extension appear to have synergistic effects on the increased risk of poor CSS in patients. This result can in the further development of treatment guidelines to improve the outcome of FTC patients.