Usefulness of cytokeratin 19 expresion in diagnosis of follicular variant of papillary carcinomna

초록

In thyroid, the diagnosis of papillary carcinoma(PC) is based on nuclear features. The follicular variant of papillary carcinoma is characterized by follicular growth pattern and tumor cells with appropriate nuclear features of PC. However, identification of these features is inconsistent and controversial. IN addition, occasnionally these lesions may show focal or multifocal instead of diffuse distribution of nuclear features of PC. Such lesions can be underdiagnosed as benign follicular nodule. Previous studies have shown that cytokeratin(CK) 19 is helpfil in differentiating PC from other benign and malignant follicular patteren lesions. In this study, we applied monoclonal antibody to CK 19 to determine the diagnostic accuracy of this marker. Formalin fixed paraffin embedded tissue from 85 surgically resected thyroid nodules included 15 nodular hyperplasia, 15 follicular adenoma, 20 follicular ccarcinoma and 35 papillary carcinoma(20; classical PC and 15 follicular variant PC). All cases of classic PC showed strong and diffuse positivity for CK19(100%). Follicular variant PCshowed strong and diffuse positivity for CK19 in 14cases(93.5%). Follicular carcinoma were positive for CK19 in 4 cases(20%) with moderate intensity. Follicular adenoma were positive for CK19 in 1 case(6.7%) with moderate intensity. Nodular hyperplasia were focally positive in most cases. Therefore, immunoreativity for CK 19 was strongly and uniformly expressed in PC including follicular variant PC. Focal CK19 immunoreactivity may be found in follicular carcinoma and benign lesion, but diffuse and stron positivity is characteristic of papillary carcinoma. This result might be of differentila diagnostic value for distinction of papillary and follicular thyroid neoplasm which sometimes have an overlapping histologic pattern.