Abstract / Summary
Background: Adjuvant radiotherapy (RT) after gross-total resection of World Health Organization (WHO) grade 2 meningioma remains an individualized decision in the absence of definitive randomized evidence. We aimed to identify the clinical, radiological, and pathological factors associated with observed adjuvant RT allocation after Simpson grade I resection and to evaluate the discriminatory performance of proliferative biomarkers in real-world multidisciplinary practice. Methods: This single-center, retrospective cohort included 65 patients, of whom 56 undergoing Simpson grade I resection constituted the primary analytic cohort. Associations with observed RT allocation were evaluated using Firth-penalized logistic regression. Ki-67 and mitotic-index discrimination was summarized using receiver operating characteristic (ROC) analysis, and Ki-67 threshold stability was assessed in 5000 bootstrap resamples. Brain invasion was evaluated in a documented-case sensitivity analysis. Results: Adjuvant RT was administered to 24 of 56 patients (42.9%). In models adjusted for age, sex, neutrophil-to-lymphocyte ratio, and tumor size, each 5-percentage-point increase in Ki-67 was associated with higher odds of RT allocation (OR 7.10, 95% CI 2.20–22.94; p = 0.001), as was each increase of 5 mitoses per 10 high-power fields in mitotic index (OR 5.81, 95% CI 2.01–16.75; p = 0.001). Ki-67 showed greater apparent discrimination than mitotic index (area under the curve [AUC] 0.925 vs. 0.801; DeLong p = 0.008). The apparent Youden-optimal Ki-67 threshold was 14%, but thresholds of 12%, 14%, and 15% were selected in 33.4%, 41.9%, and 23.1% of bootstrap samples. Among 44 patients with documented brain-invasion status, Ki-67 remained associated with RT allocation after adjustment for brain invasion (OR 4.53, 95% CI 1.77–11.63; p = 0.002). Conclusions: Ki-67 and mitotic index were associated with observed RT allocation, but both markers were already available to the tumor board. These findings describe institutional treatment-allocation patterns and do not establish RT benefit or validate a Ki-67 threshold for recommending treatment.