The absence of CD56 expression can differentiate papillary thyroid carcinoma from other thyroid lesions.

Context: The neural cell adhesion molecule CD56 is an antigen important for the differentiation of the follicular epithelium. Recent studies have reported low or absent expression of CD56 in papillary thyroid carcinoma (PTC) and its presence in normal thyroid tissue, benign thyroid lesions, and most follicular non-PTC tumors.

Aim: We wish to estimate the value of CD56 in the differentiation of PTC (including follicular variant-PTC [FV-PTC]) from other nontumoral lesions and follicular thyroid neoplasias.

Settings And Design: This was a retrospective, case-control study.

Subjects And Methods: We analyzed the expression of CD56 in normal thyroid follicular tissue, 15 nonneoplastic thyroid lesions (nodular hyperplasia, Graves' disease, and chronic lymphocytic thyroiditis/Hashimoto), and 38 thyroid follicular cell neoplasms (25 cases of PTC). The immunohistochemical reactions were performed on sections stained with anti-CD56 antibody.

Statistical Analysis Used: We used the Chi-square test, values of P< 0.05 being considered statistically significant. Risk analysis was applied on these studied groups, by calculating the odds ratio (OR) value.

Results: Our results indicated that CD56 immunoexpression had differentiated PTC from benign nonneoplastic lesions (P = 0.002), as well as from follicular neoplasias (P = 0.046). There were no significant differences regarding CD56 expression between FV-PTC and classical PTC (P = 0.436). The immunoexpression of CD56 has differentiated PTC from other thyroid non-PTC lesions (P < 0.001), with 26.4 OR value.

Conclusions: CD56 has been proved to be a useful marker in the diagnosis of PTC, including FV-PTC. Its absence can help differentiate FV-PTC from other thyroid nodules with follicular patterns.