Ewing sarcoma of the thyroid: report of 2 cases and review of the literature.

BACKGROUND Neuroendocrine tumors of the thyroid encompass a wide differential diagnosis. The most common is medullary thyroid carcinoma. One must consider other possibilities when a neuroendocrine thyroid tumor is calcitonin negative. We report 2 cases of Ewing sarcoma of the thyroid and discuss the differential diagnosis and workup of a calcitonin-negative neuroendocrine tumor of the thyroid. METHODS/RESULTS This is a retrospective review of 2 patients diagnosed with Ewing sarcoma of the thyroid and a review of the literature. CONCLUSIONS Ewing sarcoma of the thyroid is an exceedingly rare diagnosis, but should be included in the differential diagnosis for a thyroidal neuroendocrine lesion (especially in the absence of calcitonin). The use and interpretation of immunohistochemistry (IHC) and fluorescent in situ hybridization are essential in making the correct diagnosis.