Multinucleate giant cells in papillary thyroid carcinoma. A morphologic and immunohistochemical study.

Multinucleate giant cells (MGCs) occur in a variety of inflammatory, hyperplastic, and neoplastic thyroid disorders. They also have been recognized as a feature of papillary thyroid carcinoma (PTC), particularly in fine-needle aspiration biopsies (FNAB). However, the origin of the MGCs and their comparative frequencies in histologic and cytologic preparations have not been established. Therefore, histologic sections from 76 cases of PTC were examined and immunohistochemical analyses for epithelial and histiocytic markers were performed. Giant cells were identified in histologic sections of 35 cases (46%) of PTC. In cytologic preparations, MGCs were identified in 12 of 22 cases (55%). MGCs were present within follicles or adjacent to papillae, and were often associated with resorption of colloid. Immunohistochemical results indicated that MGCs were of histiocytic rather than epithelial origin. Multinucleate giant cells in PTC most likely represent a response to leakage of colloid into the interstitium. Although MGCs have been described most commonly in inflammatory conditions of the thyroid, the results of this study suggest that their presence should prompt a careful appraisal of associated PTC.