Defining Optimal Residual Tumor Volume for Survival in IDH-Wildtype Glioblastoma

Survival outcomes in glioblastoma (GBM) are influenced by age, functional status, methylguanine-DNA methyltransferase (MGMT) promoter methylation status, and extent of resection (EOR). Prior research on the EOR has focused on the degree of resection relative to the pre-operative tumor volume. Therefore, we sought to evaluate the influence of residual tumor volume (RTV) thresholds, stratified by methylation status, on survival in GBM.

In this single center, retrospective cohort study, we evaluated 237 patients with isocitrate dehydrogenase (IDH) wildtype GBM who underwent surgery from March 2011 to November 2022 by all surgeons in our department. We extracted data on patient demographics (age, functional status), molecular markers (methylation status), imaging characteristics (pre- and post-operative tumor volume), histopathological features (Ki-67 index), and treatment parameters (radiation therapy dose).

The cohort had a mean age of 61.7 years (range: 19.18-88.31). The mean preoperative tumor volume was 26.78 cm³. The mean postoperative volume was 6.00 cm³. Optimal survival was noted at a postoperative residual tumor volume (RTV) threshold of 1.75 cm³ in the full cohort. A threshold RTV of 1.75 cm³ in methylated GBM and 2.50 cm³ in unmethylated GBM conferred optimal survival benefit.

An RTV of 1.75 cm³ confers optimal survival benefit in IDH wildtype GBM. A threshold RTV of 1.75 cm³ in methylated and 2.50 cm³ in unmethylated IDH wildtype GBM confers optimal survival benefit. Our findings suggest that RTV may be a more accurate prognostic tool than EOR and could guide surgical decision-making.