Tumor characteristics and biological behavior of oligodendroglioma

Whereas in astrocytomas grading results yielded satisfying clinico-pathological correlations, grading procedures were without acclaim in the oligodendroglia! tumor group. The reason for this might be that only small series of this uncommon neoplasm were studied, and delineation of oligodendroglia! tumors from mixed gliomas or astrocytic tumors was hampered with difficulties. In order to study the relationship between tumor size and survival, as well as tumor size and histopathologic grade, tumor volumes were calculated from the CT-scans of 43 oligodendrogliomas (paper 1). Although a good correlation between grade and survival was shown, no correlation between tumor size and survival or histopathologic grade was obtained. In paper 2 a comparison was made between the traditional grading system of Kernahan, and the recently developed grading system for oligodendrogliomas of Smith. In a retrospective study on 72 patients the grading results of both systems were related to the survival times of the patients. It was found that grading according to both systems yielded three groups of patients with significant differences in survival. Nevertheless, the grading system of Smith is preferred because of its lower inter-observer error. The prognostic value of DNA-flow cytometry and mitotic count was tested retrospectively on the paraffin-embedded material of 85 oligodendrogliomas (paper 3). The results of the DNA-flow cytometry neither correlated with survival, nor with the histopathological grades. The mitotic count, however, had relevance for the prognosis. Thus, the mitotic count is a valid parameter for grading oligodendrogliomas.