Primary squamous cell carcinoma of the thyroid gland.

A case of primary squamous cell carcinoma of the thyroid is presented. Squamous epithelium is normally not present in the thyroid gland, and this tumor is exceedingly rare. Proper workup is described, including the differentiation from metastatic disease. The case reported is of a 64-year-old woman who presented with an asymptomatic nodule and underwent thyroidectomy. The final pathologic diagnosis, confirmed using immunohistochemistry for cytokeratin and transmission electron microscopy, revealed the unusual tumor. Squamous cell carcinoma of the thyroid is highly aggressive and behaves clinically like anaplastic thyroid carcinoma; the prognosis is poor. The patient described developed local recurrence and expired 7 months after resection from local invasion and airway obstruction. Unfortunately, this is the typical outcome. Chemoradiotherapy is generally not helpful, and complete resection remains the best chance for cure.