Introduction: IDH-1 mutated glioblastomas are associated with a better prognosis than glioblastomas with wild type IDH-1. Most explanations for this improved prognosis is due to these tumors responding better to therapy. Recent work has suggested they have a different behavior. Diffusion tensor imaging (DTI) is able to explore the invasive behavior of glioblastomas and can identify a number of invasive phenotypes. Approximately 20% are minimally invasive and they have improved survival. This study aims to look at differences in invasive behavior in pre-operative GBMs with IDH-1 mutation status.
Methods: Patients with resectable glioblastomas were imaged at 3T with a protocol including DTI. The DTI data was decomposed into isotropic (p) and anisotropic (q) components and these abnormalities were outlined. The difference between these regions has been previously shown to be the region of invasion and was classified according to previously published classification. The tumors were resected and the IDH-1 status assessed using immunohistochemistry for the R132 mutation.
Results: 68 patients were studied - 9 IDH-1 mutated GBMs, and 57 wild type IDH-1. All of the IDH-1 tumors exhibited minimally invasive DTI patterns. Only 5 (8%) of the IDH-1 negative tumors were minimally invasive, 14 (23%) were locally invasive and the majority 41 (69%) had a diffuse pattern of invasion. All the IDH-1 group showed tumour surrounded by intact white matter. This was confirmed by measures of the diffusion tissue signature of adjacent white matter.
Conclusions: We have shown that IDH-1 mutated GBM have a different invasive behavior compared to the non-mutated GBMs. This difference is seen at first presentation and is not related to response to therapy. This lack of invasion can help explain the better prognosis of this GBM subtype.
Patient Care: This study shows that IDH-1 positive tumors have different biology to wild type tumors. By identifying this group pre-operatively might allow more aggressive local therapy in this group.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) understand the differences in outcome with IDH-1 positive GBMs; 2) see the role of DTI in identifying the invasiveness of glioblastomas.