Follicular carcinoma of the thyroid with extensive clear-cell differentiation: A potential diagnostic pitfall

Clear‐cell features have been recognized in several different thyroid neoplasms. A case of thyroid follicular carcinoma with extensive clear‐ and Hurthle‐cell features is described in a 37‐yr‐old white female, with cytochemical and immunohistochemical analysis. The tumor of the thyroid gland, with anterior neck soft‐tissue extension, displayed clear cells on fine‐needle aspiration, which were negative for thyroglobulin. The surgical specimen displayed predominately clear cells (80%), and only the nonclear‐cell areas stained for thyroblobulin. Proper categorization of clear‐cell lesions of the thyroid and soft tissues requires a multimodality approach, involving clinical/pathological correlation, morphological analysis, and ancillary tissue studies. Immunhistochemical stains for thyroglobulin are quite definitive in making the distinction between primary clear‐cell thyroid tumors vs. metastatic clear‐cell tumors. Cytologists should be aware, however, that the clear‐cell areas of thyroid tumors might not stain for thyroglobulin. Diagn. Cytopathol. 2000;23:222–223. © 2000 Wiley‐Liss, Inc.