Abstract
INTRODUCTION: The overproduction of the oncometabolite 2-hydroxyglutarate (2HG) in IDH mutated gliomas can be detected non-invasively by magnetic resonance spectroscopy (MRS). In this study, we used two approaches for 2HG detection, e.g., difference spectroscopy (MEGA-PRESS) and conventional spectroscopy optimized for 2HG detection (PRESS), we assessed specificity and sensitivity and we related the results to patients’ natural history, 2HG tissue dosage and tumor molecular status. METHODS: Thirty patients were included: six subjects before surgery with suspected brain glioma (pre-operative cohort), and twenty-four patients affected by an IDH1 mutated glioma (post-operative cohort). IDH status was assessed for all patients combining detection of expression of IDH1-R132H mutant by immunohistochemistry (IHC) and Sanger sequencing for IDH1 and IDH2 gene mutations. Acquisitions were performed using a 3-T whole-body MRI. MRS sequences were optimized for 2HG detection: 1) a single-voxel MEGA-PRESS sequence (TR=2s, TE=68ms, 128 averages, scan time = 9 min), measuring the 2HG signal at 4.05 ppm; 2) a single-voxel PRESS sequence (TR=2.5s, TE=97ms, TE1=32ms, TE2=65ms, 128 averages, scan time = 6 min), measuring 2HG signal at 2.25 ppm. VOI size was 2x2x2 cm3, adapted to tumor size in order to minimize partial volume effects (minimum size 6 cm3). 2-HG tissue dosage was performed by gas chromatography-tandem mass spectrometry (GC-MS/MS). RESULTS: In the pre-operative cohort, 2HG was detected in five out of the six patients using MEGA-PRESS and only in two patients by PRESS. Histopathological analysis proved that all the five patients with 2HG signature on MRS, were affected by an IDH mutated gliomas (two grade II and three grade III gliomas). The patient with no 2HG signature on MRS resulted to be affected by an IDH wild-type ganglioglioma [MEGAPRESS sensitivity 100% (0.4 to 1.0, 95% CI); specificity 100% (0.02 to 1.0, 95% CI)]. In the post-operative cohort, 2HG was detected in seven out of twenty-four patients using MEGA-PRESS (sensitivity 29%), and only in three patients using PRESS (sensitivity 12%). Detection of 2HG was not associated with grade (p=0.4), histological diagnosis (p=0.5), or the fact that patients were out of treatment at the moment of MRS (p=0.2). 2HG dosages performed in tissue significantly correlated to the 2 HG quantitative measures by MRS for the five IDH mutated glioma patients scanned before surgery (r2 0.8, P 0.02). CONCLUSIONS: These preliminary results suggest that MEGA-PRESS can provide high sensitivity/specificity for prediction of IDH mutation status before surgery, in contrast to PRESS. The MRS values significantly correlate with 2HG tissue dosage by GC-MSMS. In the post-operative cohort sensitivity was lower. Factors which can affect the sensitivity of the measurement and correlations with the molecular pattern will be further analyzed in a larger cohort.