Colonic adenocarcinoma metastatic to thyroid Hürthle cell carcinoma presenting with airway obstruction.

Clinical presentation of a metastatic carcinoma to the thyroid gland is rare; it is more commonly reported in autopsy studies. Clinical presentation of malignant primary tumors to the thyroid is most common for renal, breast, and lung tumors that metastasize through a blood-borne route to the vascular thyroid gland. A 71-year-old man with a history of colon cancer that had been in remission for seven years had a long-standing thyroid goiter being followed elsewhere, with previous needle aspiration cytology consistent with a benign thyroid goiter. He presented with stridor, a 14 cm thyroid mass, and a larynx dramatically deviated to the contralateral side. Thyroidectomy resulted in return of the larynx to the midline with mobile vocal cords. Final pathologic examination indicated the rare phenomenon of tumor-to-tumor metastasis--a colon adenocarcinoma metastatic to a thyroid Hürthle cell carcinoma with focal areas of dedifferentiated anaplastic thyroid cancer. Colorectal carcinoma can remain asymptomatic for years. A thyroid mass in a patient previously diagnosed with a slow-growing malignancy (breast, kidney, colon) should be suspected of being a distant metastasis. Surgery may be indicated as palliative treatment.