Impact of Extent of Resection on Overall Survival in Glioblastomas: An Umbrella Review of Meta-Analyses

(1) Background: Glioblastoma (GBM) is the most common malignant brain tumor in adults. Due to a lack of level 1 evidence, there is no clear consensus on the optimal extent of resection to improve overall survival. This umbrella review aggregates existing meta-analyses (MAs) to assess overall survival in patients undergoing subtotal resection (STR) versus gross total resection (GTR). (2) Methods: A systematic search of PubMed, Scopus, and Web of Science identified 441 studies, with four MAs meeting inclusion criteria. Data were analyzed using the metaumbrella R package, focusing on overall survival. Quality was assessed using AMSTAR2, with scores ranging from 0 to 11. The Ioannidis criteria were applied to evaluate the credibility of the evidence. (3) Results: The quality assessment rated all four studies highly, with a mean AMSTAR2 score of 10.25. The pooled analysis revealed a significant survival advantage for GTR over STR. However, the Ioannidis classification graded the evidence as Class III, indicating weak credibility. (4) Conclusions: GTR offers a slight survival benefit over STR in GBM patients, but the credibility of the evidence is weak, highlighting the need for further research.