Carcinoma of the thyroid with ewing family tumor elements and favorable prognosis: report of a second case.

The rare reports of primary, nonneuroendocrine small cell carcinomas of the thyroid have not provided enough evidence to support the recognition of these tumors as an entity or to understand their etiopathogenesis. We report the second case of a primary, nonneuroendocrine small cell carcinoma of the thyroid displaying diffuse expression of cytokeratins, CD99, and p63, in the absence of vimentin expression, in a 24-year-old male who is alive without any signs of disease 13 years after total thyroidectomy and radioactive iodine. The tumor disclosed the EWSR1-FLI1 rearrangement, and we propose to designate it as a carcinoma of the thyroid with Ewing family tumor elements.