Prognostic implications of glial fibrillary acidic protein containing cell types in oligodendrogliomas

In oligodendroglial tumors the intermediate filament glial fibrillary acidic protein (GFAP) may be expressed by cells with the morphologic characteristics of typical oligodendrocytes (gliofibrillary oligodendrocytes [GFOC]) and by miniature forms of gemistocytes (minigemistocytes) as well. These latter cell types have been regarded as transitional cells that represent intermediate forms between an oligodendroglial and an astrocytic phenotype. Furthermore, in oligodendrogliomas GFAP may be expressed by intermingled classic large gemistocytes, which are not considered transitional cells. In a retrospective study of 111 oligodendrogliomas, the presence of the various GFAP-positive cell types was correlated with the survival rates of the patients. Therefore, GFAP expression was visualized with the use of an indirect conjugated peroxidase method. The survival times of the patients were recorded and statistical comparisons were made. The percentage of GFAP-positive tumor cells is increased in oligodendrogliomas of 28 patients who underwent a second biopsy (all these patients had been treated with radiation therapy as well). It was found that neither the presence of GFOC nor that of minigemistocytes is predictive of the survival. In contrast, patients with classic gemistocytes had survival lengths approximately twice as short as those of patients who did not have these cells in their tumors. No clear correlation was found between tumor grading or any of the individual histopathologic features with the presence of the various GFAP-positive cell types. The ominous sign of the presence of gemistocytes in oligodendrogliomas confirms some earlier reports about the prognostic significance of this cell type in astrocytomas.