The value of the immunohistochemical exam in the diagnosis of the secondary malignant tumors to the thyroid gland.

The aim of the study was to analyze several cases of secondary tumors to the thyroid, by focusing on the role of the immunohistochemical (IHC) exam in specifying the origin of the tumoral process. The studied group included 16 patients, investigated by fine-needle aspiration biopsy, frozen sections at the surgical moment, routine histopathological exam and immunohistochemical staining, using different antibodies, in accordance with the histological aspects. The final diagnosis was established as follows: metastases of squamocellular carcinoma with different degree of differentiation (seven cases), metastases of adenocarcinoma (four cases), metastases of renal cell carcinoma (two cases), metastases of Hodgkin (one case) and non-Hodgkin lymphoma (two cases). In four cases, the primary tumors were identified after the diagnosis of their metastases in thyroid. The immunohistochemical staining was useful in the diagnosis of squamocellular carcinoma metastases, poorly differentiated (CK19 positive), of renal cell carcinoma with clear cells (CK18, CK19 and CD10 positive) and in the establishing of the tumoral origin for adenocarcinomas (CK7 positive--respiratory tract, CK20 positive--digestive tract). Secondary tumors to the thyroid are rare tumors, with miscellaneous histological aspects, reason for which the diagnostic may be difficult. In these cases IHC is a useful method, allowing to the identification of the primary tumor.