Cut-point for Ki-67 proliferation index as a prognostic marker for glioblastoma

Ki-67 proliferation index (Ki-67 index) is used to quantify cell proliferation during histopathological assessment of various tumors including glioblastoma (GB).

We aimed to assess correlation between Ki-67 index and overall survival in patients with GB and determine a cut-point for Ki-67 index that predicts for poorer survival.

Records of adult patients diagnosed with GB on histopathological specimens at a tertiary cancer center in Sydney between 1 January 2002 and 30 July 2012 were retrieved. Specimens of these patients were examined for quantification of Ki-67 staining by two independent pathologists. Patient, disease, treatment, and survival data were collected from hospital and cancer care service records. Statistical analysis was performed using proportional hazards models, Kaplan-Meier curves, and the minimum P-value approach.

Of the eligible 71 patients, 58% were males with median age of 58 (range 18-87). Seventy-three percent of patients were of ECOG performance status 0-1. There was a statistically significant correlation between Ki-67 index and overall survival. In patients with Ki-67 > 22% (n = 36), 5-year survival was approximately 30% compared to 5% in those with Ki-67 ≤ 22% (n = 35; log-rank P-value = 0.04; hazard ratio (HR) = 0.53; 95% confidence intervals (CI), 0.29-0.97).

This study demonstrates a positive correlation between Ki-67 index and overall survival in patients with GB. Percentage staining of Ki-67 < 22% appears to predict for poorer survival in GB.