Immunohistochemical markers in diagnosis of papillary thyroid carcinoma: utility of HBME1 combined with CK19 immunostaining

Papillary thyroid carcinoma and its variants can be difficult to distinguish from cellular adenomatous nodules. Prior studies have advocated various antibodies to aid in the differential diagnosis, but there is little agreement on their utility. We undertook this study to evaluate immunohistochemical markers in the diagnosis and differential diagnosis of papillary thyroid carcinoma. Ten cases of papillary thyroid carcinoma were initially stained for HBME1, CK19, fibronectin1, Ki-67, Calretinin, p16, SFTPB and CITED1. Additionally, two previously untested antibodies to molecules that have been found to be upregulated in papillary thyroid carcinoma (CST6 and EPS8) were also evaluated. Of these, only HBME1, CK19 and fibronectini showed diagnostic utility. These three markers were then further evaluated in 51 papillary thyroid carcinomas and 57 benign thyroids. HBME1 was the most sensitive and specific marker, staining 49/51 papillary thyroid carcinomas and only 4/57 benign thyroids. CK19 was equally sensitive staining all 51 papillary thyroid carcinomas, but it was nonspecific staining 39 of 57 benign thyroids. A negative result, however, was helpful in excluding papillary thyroid carcinoma. Fibronectin1 was positive in 35/51 papillary thyroid carcinomas (69%) and 4/57 (7%) benign thyroids, but its utility was hampered by high background staining. These findings suggest that the combination of HBME1 and CK19 has the greatest diagnostic utility in the differentiation of papillary thyroid carcinoma from its benign mimics.