Expression of Cytokeratin 19 in the Diagnosis of Thyroid Papillary Carcinoma by Quantitative Polymerase Chain Reaction

Abstract

To examine cytokeratin 19 (CK19) expression levels by immunostaining for protein and quantitative reverse-transcription polymerase chain reaction (qPCR) for messenger RNA in thyroid surgical specimens from patients with papillary carcinoma (PC) and other types of thyroid lesions. A total of 54 randomly selected postoperative thyroid tissue samples were collected for formalin-fixed paraffin-embedded sectioning or flash-frozen total RNA extraction for complementary DNA synthesis (or both). Tissue sections were stained for CK19 expression with use of a specific monoclonal antibody. qPCR was performed on synthesized complementary DNA with sequence-specific primers for human CK19 in conjunction with ribonucleoprotein S18 for normalization. CK19 immunostaining was diffuse and intense in all PC lesions and considerably less in specimens that harbored both Hashimoto thyroiditis (HT) and PC. CK19 immunostaining was mostly absent in areas of multinodular goiter (MNG), with occasional focal staining. HT and Hürthle cell adenoma were essentially negative for CK19 immunostaining, except for weak staining in focal areas. Analysis of CK19 gene expression by qPCR revealed that the PC samples tested (n = 21) had significantly higher levels in comparison with all other groups (P < 0.0001). Furthermore, PC had a 32-fold mean level increase in CK19 expression in comparison with CK19 expression in MNG. Hürthle cell adenoma (n = 5) and HT (n = 7) lesions were similar to MNG in CK19 expression, with some overlap of CK19 between HT and PC. The data indicate that expression of CK19 by qPCR is a quantitative method for distinguishing PC lesions from other types of thyroid lesions, in contrast to the more qualitative immunohistochemistry. Moreover, qPCR of CK19 is a valid method that could be used as an ancillary tool in diagnosing thyroid cancer. The expression of CK19 by qPCR may be adopted, in combination with other markers, for molecular definition of the various subtypes of thyroid lesions assessed by fine-needle aspiration biopsy in the preoperative diagnosis of thyroid lesions.