Immunohistochemical expression of Olig2, CD99, and EMA to differentiate oligodendroglial-like neoplasms

Introduction
This study has assessed the diagnostic ability of oligodendrocyte-2 (Olig2), CD99, and epithelial membrane antigen (EMA) immunohistochemical stains to diagnose oligodendroglial-like neoplasms as central neurocytoma, ependymoma, or oligodendroglioma.

Material and methods
An immunohistochemistry (IHC) panel of Olig2, EMA, and CD99 was performed on 18 central neurocytomas, 46 ependymomas, and 28 oligodendrogliomas. A quantitative labelling index of stained tumor cells was assessed using a scoring system, and its diagnostic predictability was evaluated with multinomial logistic regression.

Results
Significant differences in IHC expression patterns were observed between all tumor groups (p < 0.001). The labeling indices of the histochemical expression of Olig2, EMA, and CD99 were related to diagnostic predictability. Olig2 was unlikely to differentiate ependymoma from central neurocytoma (p = 0.154), while EMA and CD99 were significant in diagnosing these two tumors (p < 0.05). Olig2 was a specific marker of oligodendroglioma, differentiating it from ependymoma and central neurocytoma (p < 0.001). EMA and CD99 were unlikely to differentiate oligodendroglioma from central neurocytoma (p > 0.05), but CD99 significantly differentiated ependymoma from oligodendroglioma (p = 0.022). These labelling indices were used to re-assess the diagnostic accuracy, regardless of tumor location and histology, and yielded significantly different tumor diagnoses.

Conclusions
The IHC panel of Olig2, EMA, and CD99 should be used to differentiate oligodendroglial-like neoplasms. Olig2 is a specific IHC marker to diagnose oligodendroglioma and differentiate it from ependymoma and central neurocytoma. Lack of Olig2 expression rules out oligodendroglioma and suggests the diagnosis of ependymoma rather than central neurocytoma if the EMA labelling index shows diffuse/partial expression. CD99 is considered a sensitive marker for ependymoma but not central neurocytoma.