PATTERN OF EXPRESSION OF INTERMEDIATE CYTOKERATIN FILAMENTS IN THE THYROID-GLAND - AN IMMUNOHISTOCHEMICAL STUDY OF SIMPLE AND STRATIFIED EPITHELIAL-TYPE CYTOKERATINS

The expression of simple and stratified epithelial-type cytokeratin (C K) intermediate filaments was evaluated by immunohistochemistry in a s eries of 41 papillary carcinomas, 10 follicular carcinomas, 2 poorly d ifferentiated carcinomas and 34 specimens of normal thyroid parenchyma and lymphocytic thyroiditis. The aim of the study was to establish th e CK profile of normal thyroid and thyroid carcinomas in order to clar ify the putative application of CK immunostaining in diagnostic surgic al pathology, and to evaluate whether the process of neoplastic transf ormation and tumour progression in the thyroid may be associated with any particular change in CK expression. Normal thyroid strongly expres sed simple epithelial-type CKs 7 and 18 and, to a lesser degree, CKs 8 and 19, but did not express stratified epithelial-type CKs. The same pattern was found in lymphocytic thyroiditis, though the CK 19 immunor eactivity was stronger in these lesions than in the normal thyroid. Pa pillary and follicular thyroid carcinomas shared the expression of sim ple epithelial-type CKs 7, 8, 18 and 19. Immunoreactivity for CK 19 wa s frequently stronger and more widely distributed within each particul ar tumour in papillary than in follicular carcinomas, but it could als o be detected, at least focally, in every follicular carcinoma. Strong expression of CK 19 highlighted small foci of papillary carcinoma not easily identifiable by conventional histological examination. Stratif ied epithelial-type CKs 5/6 and 13 were detected in a high percentage of papillary carcinomas, in contrast to their absence in follicular ca rcinomas and normal thyroid. The CK pattern was similar in primary and metastatic papillary carcinomas. We conclude that papillary carcinoma of the thyroid presents a distinct CK profile that may be used for di agnostic purposes.