Abstract BACKGROUND to assess the long-term benefit associated with supramarginal CE resection and to apply ReSECT criteria for extent of resection in patients with primary glioblastoma IDH wild-type. MATERIAL AND METHODS We performed a retrospective search in the institutional of Livorno Hospital for adult patients with primary GBM IDH wild-type. We assess residual tumor volumetry in the early post-operative magnetic resonance imaging by the 3dslicer software. We attributed EOR classes according to ReSECT criteria based on residual contrast and non-contrast enhancing tumor volumes. We performed multivariate analysis by Cox regression including main known prognostic factors and MGMT promoter status assessed by pyrosequencing. IDH wild-type status was defined on both IDH1 and IDH2 genes. RESULTS We identified 173 patients who underwent surgery for confirmed primary glioblastoma IDH wild-type in our institutions from 2016 and 2022. Male/female ratio was 1.6, median age at diagnosis 68 years old (yo) (range 30-83), median KPS before surgery was 80 (range 30-100) with no significant variation at the post-operative stage. Forty out of 173 (23%) patients received a supramarginal CE resection (class 1) in the whole cohort; prevalence of class 1 resection was the highest in the subgroup of patients aged ≤ 65 yo (27%) than the subgroup of >65 ≤ 75 yo (22%) and the subgroup of >75 yo (14%). The rate of class 1 resection was not different between patients with tumors located in the right and in left hemisphere (24% and 23% respectively). We analysed survival in patients treated with adjuvant RT-TMZ and found a significant longer OS in patients operated with resection class 1 (16.7 months) than other classes (p<0.0001). Long term benefit resulted the strongest in the subgroup of patients aged ≤ 65 yo (median OS 23.8 months). Multivariate analysis confirmed EOR according to the ReSECT criteria as the strongest independent predictor factor of OS (HR 0.6, p=0.004). CONCLUSION We efficiently implemented ReSECT criteria for EOR in our retrospective cohort of patients with primary GBM IDH wild-type. Supramarginal CE resection defined as no residual CE and ≤ 5 cm of nCE on the post-operative imaging emerged as the strongest predictive factor of survival.