The Ki-67 labeling index as a prognostic factor in Grade II oligoastrocytomas

Object. This study was conducted to determine whether proliferative tumor activity, as assessed using the Ki-67 immunohistochemical labeling index (LI), has prognostic utility for patients with Grade II oligoastrocytomas. Methods. The study period spans the years 1988 to 2000. In a retrospective analysis, the authors selected cases with biopsy-proven diagnoses of Grade II oligoastrocytomas on initial presentation. The authors added new patients to this group and followed all patients prospectively at the University of Virginia Neuro-Oncology Center. Twenty-three adult patients were followed for at least 1 year (median 40.3 months). Eleven patients with Grade II tumors and initial Ki-67 LIs less than 10% had a significantly longer median time to tumor progression (TTP, 51.8 months compared with 9.9 months) and a longer median survival (93.1 months compared with 16.1 months) than 12 patients with initial Ki-67 LIs of 10% or greater. Twelve patients with Grade III oligoastrocytomas had a mean TTP that was similar to the TTP of patients with Grade II tumors and high Ki-67 LIs (mean 4 months compared with 9.9 months) and duration of survival (13.3 months compared with 16.1 months). Conclusions. Patients with a Grade II oligoastrocytoma and a Ki-67 LI of 10% or greater have a much shorter TTP and potentially a poorer disease prognosis than expected - more similar to patients with a Grade III oligoastrocytoma. These results indicate that in the future a measure of proliferative activity should be taken into consideration along with the World Health Organization grading criteria for oligoastrocytomas.