title: 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.
  
  
  OBJECTIVE
  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%.
  
  
  CONCLUSIONS
  The combined use of CK19 and CD56 is helpful in discriminating papillary thyroid carcinoma and its variants from other mimicking thyroid lesions.
authors.affiliation: Department of Pathology, Faculty of Medicine, Zagazig University, Zagazig, Egypt. Electronic address: nehaleldieb@yahoo.com.
authors.forename: Nehal S
authors.initials: NS
authors.lastname: Abouhashem
authors.affiliation: Department of Pathology,Ahmed Maher Teaching Hospital, Cairo, Egypt.
authors.forename: Suzan M
authors.initials: SM
authors.lastname: Talaat
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000378:metabolism*; D019002:CD56 Antigen / Q000378:metabolism*; D002291:Carcinoma, Papillary / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation; D005260:Female; D006801:Humans; D053539:Keratin-19 / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D000077273:Thyroid Cancer, Papillary; D013961:Thyroid Gland / Q000378:metabolism / Q000473:pathology; D013964:Thyroid Neoplasms / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D019002:CD56 Antigen; D053539:Keratin-19; C522918:NCAM1 protein, human
keywords: CD56; CK19; Mimicking thyroid lesions; Papillary thyroid carcinoma