Abstract
INTRODUCTION
IDH mutant gliomas are typically slow-growing and non-contrast enhancing on MRI. Standard-of-care treatment of high risk IDH mutant tumors involves radiation followed by chemotherapy. At present, there are no large studies that have formally characterized the radiologic response of IDH mutant tumors to radiation treatment.
METHODS
We performed a retrospective review of 160 cases of IDH mutant glioma who received post-operative radiation treatment (RT) +/- chemotherapy and had follow-up MRI with T1, T1 post-contrast, T2 and FLAIR sequences available for review. We determined the mean tumor diameter, defined as the cubic root of the three largest tumor diameters, at post-surgical baseline and at 6, 12 and 24 months following RT completion. Radiologic response rate at each of these timepoints was determined using Radiologic Assessment in Neuro-Oncology-Low Grade Glioma criteria (RANO-LGG).
RESULTS
Complete analysis has been performed on a subset of cases (N = 99) and suggests that during the follow-up period of up to 2 years post-RT, the vast majority of patients with IDH mutant gliomas experience a stable disease (SD) response as defined by RANO-LGG. No minor responses (MR), defined as a 25% or less decrease in tumor area, have been observed at 1 and 2 years. Further quantitative analyses are ongoing.
CONCLUSIONS
These data indicate that RT +/- chemotherapy for IDH mutant glioma rarely results in tumor shrinkage, as measured by RANO-LGG criteria. Appropriate power for surrogate endpoints such as radiologic response rate will be critical in the design of future clinical trials examining novel therapies for newly diagnosed IDH mutant gliomas. This dataset provides a cohort that can serve as a historical comparator for future studies of novel therapeutic approaches.