Immunohistochemical study of CD99 and EMA expression in ependymomas.

Tumors of the central nervous system (CNS) represent a unique, heterogeneous population of neoplasms and include both benign and malignant tumors. The present study was carried out on a total of 79 archival cases of ependymal tumors in addition to a variety of other primary CNS tumors. The study entailed the use of CD99 monoclonal antibody and epithelial membrane antigen (EMA). It was found that all 38 ependymoma cases (classic and nonclassic) showed positive membranous and intracytoplasmic CD99 immunoreactivity. Upon comparing with other CNS tumors (41 cases), it was found that CD99 could differentiate between ependymomas and nonependymal tumors, but intensity and pattern of staining were of no consequence in determining variant type or degree of histologic aggressiveness. In regard to EMA immunoreactivity, which was restricted to the ependymoma group, 2 patterns of staining could be detected--the intracytoplasmic dotlike pattern and the ringlike pattern--but some cases were completely negative. Thus, EMA was found to be of little value in the diagnosis of ependymoma and in the differentiation between different types and grades. CD99 can hence be recommended for use as a good marker for differentiation between ependymal and other CNS tumors. EMA expression and pattern of distribution, on the other hand, cannot be employed to determine the type of variant or the degree of tumor aggressiveness, and hence cannot predict the behavior of ependymal neoplasms.