Astrocytomas represent the most frequent primary
tumors of the central nervous system. Recently, the determination of the proliferative index of astrocytic
tumors by different methods has been proposed as a valuable tool for
tumor grading and also as a prognostic marker. The aim of the present study was to evaluate the expression of cell proliferation-related
proteins in human astrocytic
tumors of different histopathological grades (WHO). An immunohistochemical study of the Ki-67, Topoisomerase IIalpha (
Topo IIalpha) and
c-MYC proteins using the
avidin-
biotin-
peroxidase method was performed in 55
astrocytomas (13 grade I, 14 grade II, 7 grade III and 21 grade IV) and five samples of non-
tumor brain tissue (control group). Ki-67,
Topo IIalpha and c-MYC positive indices tended to increase according to malignant progression, were absent in non-
tumor brain tissue and showed maximum values in high-grade
astrocytomas (III and IV). A gradual increase in
Ki-67 antigen expression was observed in agreement with mitotic index and histopathological classification. The same was not observed for
Topo IIalpha and c-MYC.
Ki-67 antigen detection in more than 8.0% of the
tumor cells distinguished
astrocytoma grade IV, while a labeling index between 1.5 and 8.0% characterized
astrocytomas grade III and values below 1.5% discriminated low-grade
tumors (I and II). These results indicate that
Topo IIalpha and c-MYC expression is associated with cell proliferation in
astrocytomas, although not in an exclusive way. Moreover,
Ki-67 antigen was found to be the best marker of cellular proliferation, and its expression predicts the grade of astrocytic
tumors.