Clear cell variant of thyroid carcinoma.

Three carcinomas composed of a variable proportion of clear cells, oxyphil cells, and cells with combined oxyphil and clear cell features are reported. Cytologically, these tumors were included in the category of oxyphil cell variant of follicular carcinoma. In regard to pattern, two were entirely follicular, and one had follicular and papillary areas. The biologic behavior of these tumors, however, was consistent with that of follicular carcinomas. The clear cell change could be the result of chronic TSH overstimulation. This may explain the variable histological patterns, nuclear features, and biologic behavior associated with these tumors. These tumors bear a striking histologic resemblance to metastatic renal cell carcinoma and clear cell neoplasms from other sites. Immunocytochemical stain for thyroglobulin proved to be a specific and sensitive method for identification of these tumors.