Usefulness of Cytokeratin 19 expression in Diagnosis of Folicular variant of Papillary Carcinoma

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 papillary carcinoma. However, identification of these features is inconsistent and controversial. In addition, occasionally these lesions may show focal or multifocal instead of diffuse distribution of nuclear features of papillary carcinoma. Such lesions can be underdiagnosed as benign follicular nodule. Previous studies have shown that cytokeratin(CK) 19 is helpful in differentiating papillary carcinoma from other benign and malignant follicular patterned lesions. In this study, we applied monoclonal antibody to CK19 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 carcinoma and 35 papillary carcinoma (PC; 20 classical PC and 15 follicular variant PC). All cases of classical PC showed strong and diffuse positivity for CK19(100%). Follicular variant PC cases showed strong and diffuse positivity for CK19 in 14 cases(93.3%). 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 for CK19 in 2 cases(13%). Normal thyroid parenchyme adjacent to the tumor nodule showed very focal positivity in most cases. There fore, immunoreactivity for CK19 was strongly and uniformly expressed in PC including follicular variant PC. Focal CK19 immunoreactivity may be found in follicular carcinoma and benign lesions, but diffuse and strong positivity is characteristic of papillary carcinoma. This result might be of differential diagnostic value for the distinction of papillary and follicular thyroid neoplasm which sometimes have an overlapping histological