Metastatic thyroid carcinoma without identifiable primary tumor within the thyroid gland: a retrospective study of a rare phenomenon

Metastatic papillary thyroid carcinoma without an identifiable primary tumor despite extensive microscopic examination of the thyroid gland is a rare but true phenomenon. We retrieved seven of such cases and described in details the clinical and pathologic features of these tumors. BRAF V600E immunohistochemistry and Sequenom molecular profile were conducted in selected cases. All patients harbored metastatic disease in the central (n=3), lateral (n=3), or both neck compartments (n=1). The histotype of the metastatic disease was papillary thyroid carcinoma (PTC, n=5), poorly differentiated thyroid carcinoma (PDTC) in association with a PTC columnar variant (n=1), and anaplastic thyroid carcinoma (ATC) in association with a PTC tall cell variant (n=1).

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