Intermediate filaments in cytological specimens of thyroid tumors.

Cytological specimens of thyroid carcinomas and follicular adenomas obtained by fine-needle aspiration biopsies or touch imprints were investigated with antibodies to keratin, vimentin, and neurofilaments. All tumors were keratin positive. In follicular adenomas as well as in papillary thyroid carcinomas, a coexpression of keratin and vimentin was detected; in follicular carcinomas, only some tumors showed coexpression of keratin and vimentin; and in medullary thyroid carcinomas, positive staining of all six tumors studied was seen with the keratin and neurofilament antibodies, with some tumors also showing coexpression of vimentin. The mechanisms of such coexpression is unclear.