Immunohistochemical study of papillary thyroid carcinoma and possible papillary thyroid carcinoma-related benign thyroid nodules

Recent immunohistochemical studies have identified different antisera that have various degrees of sensitivity and specificity for papillary thyroid c arcinoma (PTC). In this study, we performed immunostaining for CK, EMA, HBM E, CD57 and CD15 in PTC, and benign thyroid nodular lesions to compare the sensitivity and the specificity of these antisera for PTC. In addition, we studied the patterns of immunostaining of these antisera in benign nodular thyroid lesions displaying a fine chromatin pattern, foci of cells with nuc lear grooves, and optically clear nuclei. Fifty-five PTC (composed of 30 papillary variants and 25 follicular variant s), 5 follicular carcinomas, 30 follicular adenomas, and 20 thyroid nodular lesions (5 papillary variants and 15 follicular variants) were submitted f or immunostaining with CK, EMA, HBME, CD57, and CD15. CK and HBME showed the highest sensitivity and specificity for PTC when an arbitrary cutoff of more than 10% positive cells was considered as positive diagnostic immunostaining for these sera. The other antisera were less sen sitive and less specific. One case of PTC showed negative HBME but positive CD15, whereas three papillary variants and two follicular variants of beni gn thyroid nodules revealed a positive diagnostic HBME immunostaining fdr P TC and negative CK immunostaining. Any combination of positive diagnostic i mmunostaining with CK+ HBME, CK+ CD57 or CK+ CD15 has a sensitivity of 95% and specificity of 90% for PTC. Thyroid nodules with a diffuse or focal fin e chromatin pattern and focal areas with nuclear grooves or optically clear nuclei displayed immunoreactivity ranging from 0% to 50% of cells. Three o f five follicular carcinomas showed negative reactivity for HBME, CD57, and CD15. A combination of immunostaining with CK, HBME and CD57 (or CD 15) is a sens itive and specific test for PTC. This panel can be used to rule out thyroid nodules posing a diagnostic problem with PTC. Follicular adenoma and nodul es of the thyroid, with a fine chromatin pattern and focal nuclear grooves or optically clear nuclei, displayed an intermediate range of reactivity be tween reactive thyroid tissue and PTC.