Chordoid glioma of the third ventricle: Immunohistochemical and molecular genetic characterization of a novel tumor entity

Chordoid glioma of the third ventricle was recently reported as a novel tum or entity of the central nervous system with characteristic clinical and hi stopathological features (Brat et al., J Neuropathol Exp Neurol 57: 283-290 , 1998). Here, we report on a histopathological, immunohistochemical and mo lecular genetic analysis of five cases of this rare neoplasm. All tumors we re immunohistochemically investigated for the expression of various differe ntiation antigens, the proliferation marker Ki-67, and a panel of selected proto-oncogene and tumor suppressor gene products. These studies revealed a strong expression of GFAP, vimentin, and CD34. In addition, most tumors co ntained small fractions of neoplastic cells immunoreactive for epithelial m embrane antigen, S-100 protein, or cytokeratins. The percentage of Ki-67 po sitive cells was generally low (< 5%). All tumors showed immunoreactivity f or the epidermal growth factor receptor and schwannomin/merlin. There was n o nuclear accumulation of the p53, p21 (Waf-1) and Mdm2 proteins. To examin e genomic alterations associated with the development of chordoid gliomas, we screened 4 tumors by comparative genomic hybridization (CGH) analysis. N o chromosomal imbalances were detected. More focussed molecular genetic ana lyses revealed neither aberrations of the TP53 and CDKN2A tumor suppressor genes nor amplification of the EGFR, CDK4 and MDM2 proto-oncogenes. Our dat a strongly support the hypothesis that chordoid glioma of the third ventric le constitutes a novel tumor entity characterized by distinct morphological and immunohistochemical features, as well as a lack of chromosomal and gen etic alterations commonly found in other types of gliomas or in meningiomas .