Encapsulated follicular thyroid carcinoma exhibiting glandular and spindle cell components. A case report.

We describe an unusual case of a thyroid carcinoma exhibiting glandular and sarcomatous features. The tumor occurred in a 16-year-old girl. Histologic study of the resected thyroid gland revealed an encapsulated tumor composed predominantly of glandular structures and some solid areas. In the glandular areas, the tumor cells showed a cribriform growth pattern, and neither colloid secretion into the lumen nor clear-cut cytologic features suggestive of papillary or follicular thyroid carcinoma were observed. In the solid areas, tumor cells became spindled and showed a sarcomatous arrangement with occasional whorl formation. A transition from the glandular areas to the solid ones was observed. Immunohistochemical study revealed that tumor cells were positive focally for epithelial membrane antigen, cytokeratin and secretory component. Thyroglobulin was positive only in a few and limited areas of the glandular component. Calcitonin was negative throughout the tumor. The histologic and immunohistochemical evidence indicates that this tumor is of thyroid origin and is probably derived from thyroid follicular cells. The histology of this tumor is unique, so we report this case briefly.