Metastasis of Nonthyroidal Malignancies to the Thyroid Gland

OBJECTIVES: Metastasis to the thyroid gland (MTT) is uncommon, and its presentation, diagnosis, and management remain incompletely characterized. We described a contemporary institutional cohort and examined detection, diagnostic evaluation, treatment, and survival after MTT diagnosis. METHODS: We conducted a retrospective descriptive cohort study of patients with pathologically confirmed MTT who were evaluated at the Mayo Clinic in Rochester, Minnesota, from 2010 through 2025. Clinical, imaging, cytologic, pathologic, treatment, and outcome data were abstracted from the electronic health record. Survival was estimated using the Kaplan-Meier method. RESULTS: Among 42 patients, the most common primary malignancies were kidney (40.5%) and lung (23.8%). MTT was detected incidentally on staging or surveillance imaging in 66.7% and was symptomatic in 23.8%. The median interval from primary cancer diagnosis to MTT was 3.67 years and was longer for kidney cancer (8.7 y) than lung cancer (0.94 y). Most lesions were unifocal (81.0%); common ultrasound features were solid composition (50.0%) and hypoechogenicity (47.6%), but findings were nonspecific. Among 23 patients evaluated with a single fine-needle aspiration (FNA) before diagnosis, metastasis was confirmed on the first procedure in 56.5% of cases. Eighteen patients underwent surgery. The median overall survival after MTT diagnosis was ∼1.75 years; outcomes differed by surgical status, although treatment selection and disease extent preclude causal interpretation. CONCLUSIONS: MTT should be considered in patients with a new thyroid lesion and a history of malignancy. Tissue diagnosis may require repeat FNA, core-needle biopsy, and immunohistochemistry. Management should be individualized based on symptoms, primary tumor biology, extent of systemic disease, and goals of care.