Cytokeratin 19 (CK19) is one of the most frequently studied immunohistochemical markers in thyroid pathology. The results of several studies suggest that CK19 may be useful in the diagnosis of papillary carcinoma, where it has been shown to have strong diffuse cytoplasmic reactivity. However, the published results vary, and the utility of CK19 in the diagnosis of thyroid lesions is controversial. The aim of this study was to evaluate, by Western blot analysis and the enzyme-linked immunosorbent assay (ELISA), the expression of CK19 in the cytosolic fraction obtained from 125 specimens of various thyroid lesions: nodular goiters, follicular adenomas, papillary carcinomas, follicular carcinomas and anaplastic carcinomas. The analysis of CK19 expression using the ELISA showed that the majority of papillary carcinoma cases had a much higher level of CK19 than did nodular goiters and adenomas (P<0.001). Western blot analysis revealed the presence of CK19 in 66% of papillary carcinoma cases. CK19 expression was also found in 11, 22, 25 and 25% of nodular goiters, follicular adenomas, and follicular and anaplastic carcinomas, respectively. The results demonstrate that the evaluation of CK19 expression may be helpful in distinguishing papillary carcinoma from other benign and malignant thyroid nodules, but cannot by itself be used to establish a diagnosis.

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