Evaluation of malignant features in oligodendroglial tumors

Oligodendroglial tumors present us with some unsolved problems with reference to the pathological diagnosis of the malignancy, the classification, and the biological behavior.

We investigated 60 surgical specimens from 47 patients. This series contained 17 oligodendrogliomas, 4 oligo-astrocytomas, 32 anaplastic oligodendrogliomas, and 7 anaplastic oligo-astrocytomas. The simple five parameters, which are high cellularity, nuclear atypia, mitotic index, necrosis, and endothelial proliferation, were microscopically observed and we designated the sum of the positive parameters as the "histological score of malignancy" to express the histopathological degree of malignancy.

The mean values of the "histological score of malignancy" and mean MIB 1 staining indices demonstrated significantly higher values in high-grade oligodendroglial tumors than in low-grade tumors. In contrast, mean p53 staining indices did not show statistically significant differences between the low-grade and high-grade tumors. The findings of "gliofibrillary oligodendrocyte" on GFAP (glial fibrillary acidic protein) immunostain and of "chicken wire pattern" of tumor vessels on HE stain were observed significantly more frequently in high-grade oligodendroglial tumors. The malignant grade of the astrocytic components in the mixed oligoastrocytomas appeared to be correlated well with that of the oligodendroglial components. In the 12 recurrent cases, malignant transformations at the second surgery occurred in 5 of 6 patients whose diagnosis at the first surgery was a low-grade oligodendroglial tumor, with a mean interval of 111 months. Accordingly, the malignant transformations are not infrequent and require considerably long intervals in the oligodendroglial tumors.