Immunohistochemical Expression of CK19 and CD56 in Differentiating Malignant Neoplasms of Thyroid from Its Benign Mimickers

Background: Papillary formation is often observed in benign and malignant thyroid diseases, meaning that it is difficult to distinguish between benign and malignant lesions; hence, diagnosis based only on histopathology is often challenging, even in the hands of experienced pathologists. Thus, immunohistochemistry (IHC) is also essential in the diagnosis. This study aims to observe the utility of IHC markers (CK19 and CD56) in thyroid neoplasms. Methods: This cross-sectional study was conducted in the Department of Pathology at Bhagat Phool Singh Government Medical College for Women, Khnapur Kalan, Sonipat, Haryana. A total of 55 specimens, including 27 benign neoplasms and 28 malignant neoplasms, were subjected to IHC (CD56 and CK19). Results: Out of 55 thyroid neoplasm cases, 27 were benign and 28 were malignant. Immunohistochemistry CK19 was positive in 78.5% (22/28) of malignant cases, while negative in 78% (21/27) of benign cases with a significant p-value of <0.001; while immunohistochemistry for CD56 was positive in 92.6% (25/27) of benign cases, and 67.9% (19/28) of malignant cases showed loss of CD56 expression with a highly significant p-value of <0.001. The expression of CK19 was found to have 75% sensitivity and 74.1% specificity, while loss of CD56 expression was found to have 90.4% sensitivity and 73.5% specificity in differentiating malignant from benign thyroid neoplasms. Conclusion: CK19 is a specific marker for thyroid cancer, especially useful for identifying PTC and FVPTC. CD56 serves as a sensitive marker, with loss of expression indicating malignant potential, enhancing diagnostic accuracy in ambiguous cases.