Ki-67 labeling index predicts tumor progression patterns and survival in patients with atypical meningiomas following stereotactic radiosurgery

Purpose This study investigated whether Ki-67 labeling index (LI) correlated with clinical outcomes after SRS for atypical meningiomas. Methods This retrospective study examined 39 patients with atypical meningiomas who underwent SRS over a 10-year study period. Ki-67 LI was categorized into 3 groups: low (< 5%), intermediate (5%–10%), and high (> 10%). Local tumor control rates (LCRs), progression-free rates (PFRs), disease-specific survival (DSS) rates, and adverse radiation-induced events (AREs) were evaluated. Results The median follow-up periods were 26 months. SRS was performed at a median prescription dose of 18 Gy for tumors with a median Ki-67 LI of 9.6%. The 3-year LCRs were 100%, 74%, and 25% in the low, intermediate, and high LI groups, respectively ( p = 0.011). The 3-year PFRs were 100%, 40%, and 0% in the low, intermediate, and high LI groups ( p = 0.003). The 5-year DSS rates were 100%, 89%, and 50% in the low, intermediate, and high LI groups ( p = 0.019). Multivariable Cox proportional hazard analysis showed a significant correlation of high LI with lower LCR (hazard ratio [HR], 3.92; 95% confidence interval [CI] 1.18–13.04, p = 0.026), lower PFR (HR 3.80; 95% CI 1.46–9.88, p = 0.006), and shorter DSS (HR 6.55; 95% CI 1.19–35.95, p = 0.031) compared with intermediate LI. The ARE rates were minimal (8%) in the entire group. Conclusion Patients with high Ki-67 LI showed significantly more tumor progression and tumor-related death. Ki-67 LI might offer valuable predictive insights for the post-SRS management of atypical meningiomas.