Liposarcoma of the thyroid gland. Fine-needle aspiration cytology, immunohistology, and ultrastructure.

A 56-year-old woman presented with a rapidly growing tumoral mass of the thyroid. In fine-needle aspirates, neoplastic cells were interpreted as undifferentiated (anaplastic) carcinoma. In contrast, histologic examination of tissue samples revealed a tumor with features suggestive of myxoid liposarcoma. The non-epithelial nature was confirmed by immunohistochemical and electron microscopic evaluation. Immunostains for vimentin and S-100 protein were positive, whereas no reactivity was obtained for epithelial markers. Ultrastructurally, the tumor consisted of poorly differentiated mesenchymal cells and lipoblastic elements in various stages of differentiation. Review of the literature reveals only one previous report of thyroid liposarcoma, the diagnosis of which was based on conventional light microscopic studies.