Combined squamous cell carcinoma and follicular carcinoma of the thyroid.

Primary squamous cell carcinoma of the thyroid (PSCCT) is a malignant epithelial tumor, composed entirely of cells with squamous differentiation and accounting for fewer than 1% of all malignancies of the thyroid gland [1]. Because squamous cells are absent from the normal thyroid gland, the etiology of PSCCT remains unclear. Hypotheses include the differentiation of squamous cells derived from embryonic remnants of epithelial cells in the gland, squamous metaplastic changes in response to inflammatory diseases such as thyroiditis, and malignant neoplasms, such as papillary, follicular, or anaplastic carcinoma [2]. Occasionally, PSCCT arises from other thyroid diseases such as Hashimoto’s thyroiditis, tall cell variant papillary carcinoma, follicular carcinoma, and anaplastic carcinoma [3,4]. We describe a patient with the combination of a well-differentiated squamous cell carcinoma and follicular carcinoma of the thyroid. To our knowledge, this is the third report of a patient with primary squamous cell carcinoma plus follicular carcinoma of the thyroid in the English language literature [2,5].