Survival Comparison of Incidentally Found versus Clinically Detected Thyroid Cancers: An Analysis of a Nationwide Cohort Study

BACKGROUND: The true benefit of thyroid cancer screening is incompletely understood. This study investigated the impact of ultrasound screening on thyroid cancer outcomes through a comparison with symptomatic thyroid cancer using data from a nationwide cohort study in Korea. METHODS: Cox regression analysis was performed to assess the hazard ratios (HRs) for all-cause and thyroid cancer-specific mortality. Considering the possible bias arising from age, sex, year of thyroid cancer registration, and confounding factors for mortality (including smoking/drinking status, diabetes, and hypertension), all analyses were conducted with stabilized inverse probability of treatment weighting (IPTW) according to the route of detection. RESULTS: Of 5,796 patients with thyroid cancer, 4,145 were included and 1,651 were excluded due to insufficient data. In comparison with the screening group, the clinical suspicion group was associated with large tumors (17.2±14.6 mm vs. 10.4±7.9 mm), advanced T stage (3–4) (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.09 to 1.41), extrathyroidal extension (OR, 1.16; 95% CI, 1.02 to 1.32), and advanced stage (III–IV) (OR, 1.16; 95% CI, 1.00 to 1.35). In IPTW-adjusted Cox regression analysis, the clinical suspicion group had significantly higher risks of all-cause mortality (HR, 1.43; 95% CI, 1.14 to 1.80) and thyroid cancer-specific mortality (HR, 3.07; 95% CI, 1.77 to 5.29). Mediation analysis showed that the presence of thyroid-specific symptoms was directly associated with a higher risk of cancer-specific mortality. Thyroid-specific symptoms also indirectly affected thyroid cancer-specific mortality, mediated by tumor size and advanced clinicopathologic status. CONCLUSION: Our findings provide important evidence for the survival benefit of early detection of thyroid cancer compared to symptomatic thyroid cancer.