CK19 IS A USEFUL MARKER IN DISTINGUISHING FOLLICULAR VARIANT OF PAPILLARY THYROID CARCINOMA FROM BENIGN THYROID LESIONS WITH FOLLICULAR GROWTH PATTERN

Context. Thyroid cancer is the most common endocrine malignancy. Within various subtypes of thyroid neoplasms, those with follicular growth pattern usually make diagnostic problems. Objectives. To examine ck19 expression as a diagnostic marker in thyroid neoplasms with follicular growth pattern. Design. In this cross sectional study, 86 patients were enrolled. Subjects and Methods. Totally 22 follicular adenoma (FA), 18 well differentiated tumors with undetermined malignant potential (WT-UMP) and 46 follicular variants of papillary thyroid carcinoma (FV-PTC) were enrolled and examined for Ck19 expression by immunohistochemistry staining. Membranous/cytoplasmic staining patterns were considered as positive. Specimens without staining were considered as 0, <5% positively stained cells as 1+, 5%-25% as 2+, 25%-75% as 3+ and >75% as 4+. Result. CK19 was negative in most cases of FA while positive in most WDT-UMP and FV-PTCs, p<0.001. Additionally, most cases with 2+ and 3+ staining patterns were FV-PTC (75% and 81%, respectively, p<0.001) and none of FAs showed 3+ positivity (p<0.001). Additionally, most of strongly positive results in patients > 45 y/o were PTC (p<0.001). Conclusion. Ck19 is a useful marker in differentiating FA from FV-PTC. We found diffuse and strong (3+) staining pattern in FV-PTC but none of FAs were so. We concluded that diffuse and strong staining for ck19 in a thyroid lesion with follicular pattern of growth, especially in a patient older than 45 y/o should raise the possibility of malignancy.