Low expression of Ki-67/MIB-1 labeling index in IDH wild type glioblastoma predicts prolonged survival independently by MGMT methylation status

PURPOSE: The Ki-67/MIB-1 labeling index (LI) is clinically used to differentiate between high and low-grade gliomas, while its prognostic value remains questionable. Glioblastoma (GBM) expressing wild-type isocitrate dehydrogenase IDH(wt), a relatively common malignant brain tumor in adults, is characterized by a dismal prognosis. Herein, we have retrospectively investigated the prognostic role of Ki-67/MIB-1-LI in a large group of IDH(wt) GBM. METHODS: One hundred nineteen IDH(wt) GBM patients treated with surgery followed by Stupp’s protocol in our Institution between January 2016 and December 2021 were selected. A cut-off value for Ki-67/MIB-1-LI was used with minimal p-value based approach. RESULTS: A multivariate analysis showed that Ki-67/MIB-1-LI expression < 15% significantly correlated with a longer overall survival (OS), independently from the age of the patients, Karnofsky performance status scale, extent of surgery and O(6)-methylguanine (O6-MeG)-DNA methyltransferase promoter methylation status. CONCLUSIONS: Among other studies focused on Ki-67/MIB-1-LI, this is the first observational study showing a positive correlation between OS of IDH(wt) GBM patients and Ki-67/MIB-1-LI that we propose as a new predictive marker in this subtype of GBM.