The Value of Cytokeratin-19 Immunohistochemistry in the Differential Diagnosis of Papillary Thyroid Carcinomas

Objective: The gold standard for diagnosis of papillary thyroid carcinoma is conventional histology, which depends on the characteristic nuclear features, regardless of whether papillary architecture is present or not. This study was carried on to evaluate the utility of cytokeratin-19 in the diagnosis and differential diagnosis of papillary thyroid carcinoma. Material and Methods: Expression of cytokeratin-19 was tested on formalin-fixed, paraffin-embedded tissues from 380 surgically resected thyroid lesions including hyperplasic nodules (n = 243), granulomatous thyroiditis (n = 3), lymphocytic (n = 53) and Hashimoto's thyroiditis (n = 11), follicular adenomas (n = 17), Hurthle cell adenomas (n = 4), well-differentiated thyroid tumor with follicular architecture of uncertain malignant potential (n = 1), papillary carcinomas (n = 45), follicular carcinoma (n = 1), insular carcinoma (n = 1), and medullary carcinoma (n = 1). The immunoreactivity was scored as negative, 1+, 2+, 3+, and 4+, based on the extent of the reaction regardless of previous diagnosis. Results: Positive reaction with cytokeratin-19 was denoted in all of the 45 cases of papillary carcinomas with scores of 4+, 3+ and 2+ and the ratios were 57.8% (26/45), 33.3% (15/45) and 8.9% (4/45), respectively. There seemed to be a strong diffuse cytoplasmic reactivity with cytokeratin-19 in papillary thyroid carcinomas, The sensitivity and specificity for cytokeratin-19 in papillary carcinomas among neoplastic thyroid lesions were 91.8% and 86.2%, respectively. Conclusion: In addition to careful histological evaluation, cytokeratin-19 seems useful for the diagnosis of papillary thyroid carcinomas.