Sixteen
choroid plexus tumors (CPTs) have been investigated for the localization of different immunocytochemical markers of epithelial and nonepithelial nature, namely, simple epithelial-type cytokeratins,
vimentin,
glial fibrillary acidic protein (GFAP), a panepithelial
antigen defined by the lu-5
monoclonal antibody (lu-5 antigen),
S-100 protein, and
epithelial membrane antigen (EMA).
Intermediate filament proteins have been identified in
paraffin sections of 14 of 16 cases (87.5%). In all these
tumors, cytokeratins and
vimentin were constantly coexpressed by the neoplastic cells, in a manner similar to that of the cells lining normal choroid plexus. In 7 of these 14 cases, in addition to cytokeratins and
vimentin, the neoplastic cells were shown to coexpress GFAP, which is not synthesized by their normal cell counterpart. The appearance of GFAP immunoreactivity in CPTs might be related to an ependymal differentiation of the neoplastic cells, because normal ependyma and
ependymomas constantly coexpress GFAP and
vimentin. The simultaneous expression of three distinct
intermediate filament proteins by the same neoplastic cells is an exceedingly rare phenomenon, which has never been reported by double labeling technique in
neoplasms of the central nervous system. Despite the complex antigenic profile of the
CPT, which includes immunoreactivity for lu-5
antigen,
S-100 protein, and EMA in most of the cases, positivity for three different epithelial markers indicates that these
tumors have an epithelial nature. Moreover, the immunocytochemical typing of
CPT with the panel of
antibodies used in the current investigation allows differentiation from other primary and metastatic
central nervous system tumors.