Follicular adenoacanthoma of the thyroid gland.

A 67-year-old euthyroid black woman presented with a painful palpable thyroid nodule. Microscopic examination revealed an extensively infarcted follicular carcinoma with minimal capsular and vascular invasion and advanced squamous metaplasia. From the regions of squamous metaplasia, ultrastructural analysis demonstrated both squamous and adenomatous features within the same individual cells. We stress the prognostic importance of histologic distinction between adenoacanthomas and adenosquamous or squamous cell carcinomas. The literature is reviewed and the aetiology, pathology, classification and prognosis of primary thyroid cancers with squamous epithelium are discussed.