Glial fibrillary acidic protein (GFAP) in oligodendroglial tumors: gliofibrillary oligodendroglioma and transitional oligoastrocytoma as subtypes of oligodendroglioma.

Immuno-reactivity to glial fibrillary acidic protein (GFAP) is mainly regarded as a sign of astroglial histogenesis and/or differentiation. The presence of astrocytes in oligodendrogliomas is a well known phenomenon; in addition, GFAP-positive neoplastic oligodendrocytes have also been described but have not yet been studied systematically. Using an anti-GFAP serum in the peroxidase-antiperoxidase antiperoxidase (PAP) technique, 50 oligodendrogliomas and 16 mixed oligodendrocytomas were investigated; they had been diagnosed by routine histological stains. In half of all oligodendrogliomas, and only in a few (12%) of the mixed oligoastrocytomas, GFAP-positive oligodendrocytes were found in some areas of the classical honey-comb texture with a prominent vascular stroma. The term 'gliofibrillary oligodendrocyte' (gfoc) is proposed for these immuno-reactive cells. The existence of a tumour cell combining morphological characteristics of oligodendroglia with GFAP production in its cytoplasm may be considered analogous to transient GFAP expression by myelin-forming glia during normal development (Choi and Kim 1984), thus suggesting the return to a foetal behaviour by some neoplastic oligodendrocytes. Three tumours of the present series consisted largely of gfocs and, therefore, may be termed gliofibrillary oligodendrogliomas. In about 32% of all oligodendrogliomas, but only once in the mixed tumour group, a gradual morphological transition from gfocs to gemistocytic astrocytes was observed.(ABSTRACT TRUNCATED AT 250 WORDS)