Comparison of E-cadherin and CD56 Expression in Papillary Thyroid Carcinoma and Non-Neoplastic Thyroid Lesions

Introduction: Papillary Thyroid Carcinomas (PTC) are the most common among thyroid malignancies. The incidence of this tumour is rapidly increasing around the world. Kerala has the highest incidence of this tumour in India. Abnormalities in adhesion molecules, E-cadherin and CD56 have recently been implicated in thyroid tumourigenesis. Sometimes the diagnosis of PTC is difficult, as there are a good number of histological variants and some may be encapsulated. In such situations, evaluation of the expression of adhesion molecules like E-cadherin and CD56 are useful in accurate diagnosis. Aim: To study the Immunohistochemical Expression of E-cadherin and CD56 in PTC, its adjacent normal thyroid tissue and other non-neoplastic thyroid lesions. Materials and Methods: This was a descriptive study conducted at Amala Institute of Medical Sciences, Thrissur from January 2018 to June 2019. Seventy six thyroidectomy specimens (38 each of PTC and Non-neoplastic lesions) were studied after satisfying the inclusion and exclusion criteria. Microscopic examination of the Haematoxylin and Eosin stained sections were done for selecting the representative tissue block to immunostain for E-cadherin and CD56. Statistical analysis was performed using Chi-square test and Fisher's-exact tests. P-value of <0.05 was considered as significant. Results: E-cadherin expression was negative in 37 cases of PTC. Only two non-neoplastic lesions were negative for E-cadherin( p-value of 0.021). No significant correlation was observed between E-cadherin expression and poor prognostic factors (tumour diameter, multifocality, extrathyroidal extension and lymph node metastasis). All PTC cases showed negative CD56 expression. A total of 34 out of 38 Non-neoplastic cases showed positive CD56 staining (significant p value=0.011). In non-neoplastic lesions, E-cadherin and CD56 were preserved. CD56 showed highest specificity (100%). Conclusion: PTC was characterised by decreased or absent expression of E-cadherin as compared to the adjacent thyroid tissue. CD56 expression was uniformly negative in all the PTC cases. CD56 marker had highest specificity (100%). In follicular patterned thyroid lesions, CD56 as a single marker may be useful for identifying PTC from other thyroid lesions in daily practice. To conclude, CD56 negativity and E-cadherin loss can assist in decision making of difficult cases.