The Differences in Distant Metastatic Patterns and Their Corresponding Survival Between Thyroid Cancer Subtypes

Abstract Introduction: Distant metastasis (DM) at presentation is one of the important prognostic factors in thyroid cancers. Dissemination patterns of different thyroid cancer subtypes are still controversial. This study aimed to systematically elucidate the metastatic patterns and their corresponding survival of each thyroid cancer subtype at time of diagnosis. Methods: We accessed the Surveillance, Epidemiology, and End Results (SEER) database from 2010-2018 to search for primary thyroid cancers with DM at presentation (M1). Results: We included 2,787 M1 thyroid cancers for statistical analyses and the incidence of DM at presentation was 2.4%. Lung was the most common metastatic site for anaplastic thyroid carcinoma (ATC), poorly-differentiated thyroid carcinoma (PDTC), papillary thyroid carcinoma (PTC), and oncocytic (Hurthle) cell carcinoma (HCC) whereas bone is the favorable disseminated site of follicular thyroid carcinoma (FTC) and medullary thyroid carcinoma (MTC). The risk of liver metastasis was highest in MTC while metastases to the brain were uncommon among thyroid cancer subtypes. Among M1 thyroid cancers, ATC showed the worst outcome while PTC and FTC exhibited a superior survival. Patients with multi-organ metastases had the worst survival whereas bone metastases were associated with a favorable outcome (p < 0.001). We identified significant risk factors associated with multi-organ metastases including non-Caucasian race, large tumor diameter, ATC/FTC/MTC histology, and unifocality. Conclusion: There are significant differences in DM patterns of thyroid cancer subtypes and their corresponding survival. These clinical data could be useful for clinicians to better evaluate risk stratification and predict patient outcomes.