Squamous cell carcinoma of the thyroid: a report of two cases.

Two patients with squamous cell carcinoma, which accounts for 1.1% of all primary thyroid carcinomas, are described. Squamous metaplasia is the most likely etiology, but an occasional carcinoma may be derived from remnants of embryonic origin. Although squamous metaplasia has been documented in several conditions involving the thyroid, no evidence exists that this predisposes to squamous cell carcinoma. Metastases and direct extension of squamous cell carcinoma in the thyroid gland are much more frequent than primary involvement and are always part of a generalized carcinomatosis. A primary lesion must always be sought; however, diagnosis may not be possible until an initially occult tumor becomes evident or even until autopsy. Because this lesion typically runs a fulminant course, radical surgical resection at the earliest opportunity offers the best hope for cure. The lesions are usually radioresistant, and chemotherapy has not been shown to alter the course of this disease.