The distinction of uncommon types of thyroid carcinomas is important, because their treatment and prognosis differ. The aim of this study was to describe retrospectively the immunohistochemical profile of uncommon types of thyroid carcinomas and mode of treatment. Of the 1194 patients with thyroid carcinomas treated in Rabin Medical Center from 1954 to 2001, 153 were uncommon types (not papillary or follicular carcinomas). Specimens from archival tissue obtained from thyroidectomies in all these cases were revised and immunohistochemically examined. Anaplastic carcinomas (n=59) were positive for high molecular weight cytokeratin (CK HMW), low molecular molecular weight cytokeratin (CK LMW), cytokeratin (CK) 7, CK 8 and 18, thymoglobulin, EMA and vimentin; medullary carcinomas (n=39) were positive for CK LMW, CK 19, CK 8 and 18, CK 10, CK 7, carcinoembryonic antigen (CEA) and calcitonin; Hurthle cell carcinomas (n=30) for CK LMW, CK 19, CK 8 and 18, thyroglobulin, epithelial membrane antigen (EMA) and CEA; squamous cell carcinomas (SCC) (n=12) for CK HMW and cytokeratin total (CKs); lymphomas (n=7) for leukocyte common antigen (LCA) and B-cells (CD 20), and clear cell carcinomas (n=6) for CK LMW, CEA and thyroglobulin. Use of an immunohistochemical panel has diagnostic value in the differentiation of uncommon types of thyroid carcinoma, which help to plan the best mode of treatment.

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