Diagnostic utility of CK19 and CD56 in the differentiation of thyroid papillary carcinoma from its mimics

Abstract

Background: Papillary Thyroid Carcinoma (PTC) is the most common type of malignant thyroid tumors. The main diagnostic clue of PTC is the presence of its characteristic nuclear features. Yet, the focal presence of these features in other thyroid lesions causes a diagnostic dilemma.

Aim: To evaluate Cytokeratin 19 (CK19) and CD56 immunostains as useful diagnostic markers in distinguishing papillary thyroid carcinoma from other mimicking thyroid lesions.

Methods: Eighty cases of different thyroid lesions were submitted for immunohistochemical staining of CK19 and CD56. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy were analyzed.

Results: CK19 was expressed in 87.8% and 21.2% of the PTC group and the non-papillary carcinoma (NPTC) group respectively, with significant difference (P<0.001). CD56 expression was lost with 81.8% of the PTC group. However, CK19 was negative in only 12.7% of the NPTC group, with significant difference (P<0.001). Comparing papillary carcinoma with papillary hyperplasia, CK19 was the most sensitive immunostain and CD56 was the most specific one, with better diagnostic accuracy in combining both immunostains. Co-expression of CK19/CD56 provided 100% sensitivity and 92% diagnostic accuracy in differentiating follicular variant of PTC from follicular adenoma. Comparing FVPTC with follicular carcinoma, sensitivity and diagnostic accuracy increased to 100% and 91.7% respectively. On distinction between papillary carcinoma (Hurthle cell variant) and Hurthle cell adenoma, sensitivity, specificity, and diagnostic accuracy were 100%, 75% and 83.3% respectively, with CK19/CD56 staining combination. Comparing papillary carcinoma on top of Hashimoto's thyroiditis with Hashimoto's thyroiditis, co-expression of both markers was associated with 100% specificity, as well as increase in PPV and diagnostic accuracy to 91%.

Conclusion: The combined use of CK19 and CD56 is helpful in discriminating papillary thyroid carcinoma and its variants from other mimicking thyroid lesions.

Keywords: CD56; CK19; Mimicking thyroid lesions; Papillary thyroid carcinoma.