Impact of Lung Metastasis versus Metastasis of Bone, Brain, or Liver on Overall Survival and Thyroid Cancer-Specific Survival of Thyroid Cancer Patients: A Population-Based Study

SIMPLE SUMMARY: Patients with thyroid cancer have different survival rate based on their cancer type and the organs affected by the metastases. About 88% of the patients with follicular thyroid cancer are still alive 15 years after diagnosis. Still, some patients will develop metastasis, and the location of the metastases could indicate patients with more aggressive disease. ABSTRACT: We investigate the impact of lung metastasis versus metastasis of bone, brain, or liver on overall survival (OS) and thyroid cancer-specific survival (TCSS) in patients with thyroid cancer (TC). Therefore, de-identified SEER 18 registry data of primary TC patients diagnosed between 2010 and 2016 were analyzed. The primary outcome was the prognosis of TC patients with lung metastasis compared with other sites. The secondary outcomes included the prognosis comparison between patients with and without surgery and between single and multiple metastasis sites. Isolated lung metastasis was associated with worse OS and TCSS than bone metastasis (both p < 0.05) and was associated with worse OS than liver metastasis (p = 0.0467). Surgery performed either for the primary or distant site was associated with better OS and TCSS in patients with metastasis of lung or bone (p < 0.05). Isolated lung metastasis was related to better OS and TCSS than lung–liver, lung–brain, and lung–other multiple metastases. The multivariable analysis revealed that age < 55 years, surgery to the primary site, and to the distant site(s) were associated with better outcomes, while T4 and Tx were associated with worse outcomes. Nevertheless, it revealed that the other race (i.e., any race other than white, black, or unknown) and male gender were associated with better TCSS only (p < 0.05). Isolated lung metastasis is associated with a worse prognosis in TC patients compared with bone or liver metastasis. Surgery performed either for the primary or distant site(s) is associated with better survival outcomes in TC patients with metastasis of lung or bone.