Diagnostic utility of CD56 immunohistochemistry in papillary carcinoma of the thyroid

The marker pattern and intensity of staining were scored. Positive expression of the markers in 10% or more of follicular epithelium within the tumor or lesional cells was considered positive. An expression of <10% was considered to be negative. Diffuse CD56 expression was consistently present in normal, lesional, and neoplastic follicular epithelium, except for PTC, including the follicular variant. We concluded that CD56 is of value to distinguish PTC from other thyroid follicular pathology/histology with a sensitivity of 100% and a specificity of 100%. We suggest that CD56 is extremely useful in the diagnosis of PTC, including the follicular variant, and to distinguish it from other follicular cell-derived thyroid tumors/lesions. Application of CD56 by a group of expert pathologists on a larger series of follicular thyroid neoplasms of uncertain malignant potentials may potentially provide an objective diagnostic tool.