PurposeThe aim of this study is to investigate the association between postoperative tumor volume and overall survival (OS) of O-6-methylguanine DNA methyltransferase (MGMT)-unmethylated glioblastoma patients.MethodsOne hundred-twenty-six patients with MGMT-unmethylated glioblastoma who were treated either with surgical resection or needle biopsy between 2006 and 2015 were included in this retrospective cohort. Pre- and postcontrast T1 weighted images were evaluated in order to determine pre- and postoperative contrast-enhancing tumor volumes (CE-TV). Cox regression models adjusted for other significant prognostic factors were used to investigate the association between postoperative tumor volume and survival.ResultsComplete resection of CE-TV was significantly associated with longer OS in the univariate analysis (HR 0.61; 95% CI 0.40-0.94; p=0.02). However, this fact could not be confirmed after adjusting the model for other relevant prognostic factors (HR 1.01; 95% CI 0.65-1.55; p=0.962). Postoperative CE-TV was significantly associated with survival in both univariate (HR: 1.04; 95% CI 1.025-1.055; p<0.001) and multivariate analyses (HR: 1.027; 95% CI 1.005-1.049; p=0.014).ConclusionsAlthough complete resection of tumor tissue was not significantly associated with longer OS in MGMT-unmethylated GBM patients, maximum safe resection should always be attempted, since postoperative tumor volume is strongly associated with OS.