Papillary thyroid tumors: Diagnostic value of CD56 and Cytokeratin 19.

Introduction: Noninvasive Follicular Thyroid Neoplasm With Papillary-like Nuclear Features (NIFTP) is a tumor composed exclusively of follicles lined by cells having nuclear characteristics of papillary carcinoma. Morphological diagnosis is often difficult especially in the cases in which these nuclear abnormalities are focal.

Aim: To investigate the contribution of the immunohistochemical study with anti CD56 and anti cytokeratin 19 in the positive diagnosis of NIFTP.

Methods: This is a diagnostive, retrospective study of 40 thyroid specimens including 15 NIFTP, 10 classical form papillary carcinoma (CPC) and 15 vesicular adenomas (AV), collected over a period of eighteen months (December 2013-May 2015).

Results: Negativity with anti-CD56 was noted in 16 cases: 9 cases of NIFTP and 7 cases of CPC. A diffuse staining was noted in 14 cases of AV. Positivity with anti-Cytokeratin19 was noted in 38 cases: 14 NIFTP, 10 CPC and 14 AV. For the diagnosis of NIFTP, the sensitivity of CD56 was 60% and specificity of 100%. The sensitivity of the Cytokeratin 19 was 93,3 % and specificity of 33,3%.

Conclusions: Considering the good sensitivity and specificity of the CD56, it is possible to apply immunohistochemistry for definitive diagnosis of NIFTP and to differentiate it from adenoma. The cytokeratin 19 does not have a big contribution to distinguish between benign and malignant lesions.