Primary squamous-cell carcinoma of the thyroid gland: new evidence in support of follicular epithelial cell origin.

Primary squamous-cell carcinoma (SCC) of the thyroid gland is extremely rare. We had an opportunity to treat two such cases recently. Two elderly females presented with left lobe thyroid swelling that had a history of long-standing goiter. Fine-needle aspiration (FNA) of the thyroid nodule was done in both cases. FNA cytology showed an thyroid abscess in the first, and a Hürthle-cell neoplasm in the second case. Histopathologic diagnosis was a well-differentiated squamous-cell carcinoma with an adjacent area of lymphocytic thyroiditis in the first case, and a moderately differentiated squamous-cell carcinoma in association with a Hürthle-cell adenoma in the second case. Serial sections of the excised gland ruled out any other associated thyroid malignancy. Immunostaining for pan-cytokeratin, thyroglobulin, and calcitonin were performed. The tumor, comprising polygonal and spindle cells, showed positive staining for cytokeratin and thyroglobulin; however, calcitonin did not stain any structures. Exhaustive clinical, endoscopic, and radiological examinations, i.e., X-ray of the chest, contrast-enhanced computer tomography (CECT) of the neck and chest, and ENT checkup in both cases did not reveal any primary site of squamous-cell carcinoma as the likely source of the metastases, or any contiguous spread from neighboring structures. Both patients had ipsilateral nodal metastases, and both succumbed to the disease within 6 mo of histological diagnosis. The interesting observation in both cases was thyroglobulin positivity, indicating a follicular epithelial cell origin of the SCC.