The growth potential of ependymomas with varying grades of malignancy measured by the Ki-67 labelling index and mitotic index.

The prognostic significance of histopathological grade for postoperative outcome is not yet known for ependymomas. Data on proliferation kinetics of these tumors are few. In our study, the growth fraction was immunohistochemically determined by labelling cell nuclei with the monoclonal antibody Ki-67 in 24 tumors of the ependymoma group (2 malignant ependymomas grade III, 11 ependymomas grade II, 8 spinal ependymomas, and 3 subependymomas). The results were compared with the mitotic index in the same tumor areas. Both growth parameters are related to the grade of malignancy. The differences between the results of spinal ependymomas (grade I) and of intracranial tumors (grade II) were statistically significant. Malignant ependymomas had the highest values. Variable growth potentials could be demonstrated in a few tumors. A non-linear relationship between growth fraction and mitotic index was found, indicating a variable generation time in ependymomas (as in astrocytomas). Thus, with rising grade of malignancy the growth fraction increases and the generation time decreases.