Phenotypic characteristics of GFAP-immunopositive oligodendroglial tumours Part I: immunohistochemical study

Oligodendrogliomas are believed to derive from oligodendrocyte lineage but the expression of different immunohistochemical markers indicates some variability in their differentiation potency. It has been documented that some heterogeneity of the tumour cells exists and that oligodendrogliomas can display a spectrum of histological, immunohistochemical and fine structural features. The expression of glial fibrillary acidic protein (GFAP) in various types of neoplastic cells in oligodendroglial tumours has been well established, however the nature of these cells in relation to tumour malignancy remains controversial. The current histopathological and immunohistochemical study (with a panel of antibodies for GFAP, vimentin, S-100 protein, MBP, NSE) has been performed on biopsy specimens from 12 cases of GFAP-immunopositive oligodendroglial tumours to evaluate their phenotypic characteristics. The majority of tumours showed a variable pattern of GFAP expression in morphologically different tumour cells responding to typical neoplastic oligodendrocytes (gliofibrillary oligodendrocytes-GFOC), miniature form of gemistocytes (minigemistocytes) and neoplastic or reactive astrocytes. The majority of cases exhibited negative staining for vimentin whereas there was no evident correlation between GFAP expression and other immunohistochemical markers. The present immunohistochemical findings support the opinion that the majority of GFAP-positive neoplastic cells in oligodendroglial tumours represent the transitional cell types between oligodendroglial and astrocyte lineage. The difficulties in differential diagnosis of oligodendroglial tumours exhibiting the various patterns of GFAP expression are emphasised.