A recent study by the American College of Radiology Imaging Network (ACRIN 6684) entitled Multicenter, phase II assessment of tumor hypoxia in Glioblastoma using 18F Fluoromisonidazole (FMISO) with PET and MRI was to determine the association of baseline 18F-FMISO PET uptake and MRI parameters with 1 year overall survival (OS-1) and 6 month progression free survival (PFS-6) in participants with newly diagnosed glioblastoma (GBM). One of the pathologic hallmarks of GBM is tumor hypoxia, a potent stimulator of angiogenesis ¹. In addition, hypoxia limits the efficacy of radiation and chemotherapy and may select for a more aggressive tumor phenotype. The ACRIN 6684 trial enrolled 50 patients with newly diagnosed GBM from 11 academic centers in the United States, of which 42 had evaluable imaging studies. The primary aim analysis demonstrated that increased tumor hypoxia (18F-FMISO hypoxic volume), tumor perfusion (CBV and CBF), and vascular permeability (Ktrans) were predictive of poorer outcomes ². The goal of this study was 1) to test whether MR spectroscopy measures was predictive of outcome, and 2) to evaluate how MRS measures relate to (or complement) the previously analyzed MRI and PET markers.3D MRSI was performed using either Philips or GE 3T scanners or Siemens 1.5T or 3T scanners. Acquisition parameters included TE=135–144 ms, TR=1140–1180 ms, phase encoding=12x12x8 (12x11x3 for Philips), and a FOV of >160. Spectroscopic raw data were analyzed using LC Model software to determine the quantities of the metabolites N-acetylaspartate (NAA), creatine (Cr), choline (Cho), and lactate (Lac). For spectra classification MRSI data were overlaid on the post-contrast T1-weighted images. Voxels were classified into (i) enhancing tumor; (ii) non-enhancing peritumoral parenchyma (periphery); and (iii) contralateral normal white matter, and mean metabolite ratios in those regions were calculated as previously described ³. T1 post contrast, FLAIR, DSC, and DCE MRI data were also acquired. Receiver operating characteristic (ROC) curves for the spectroscopic markers NAA/Cho, Cho/Cr and Lac/Cr were constructed for two binary outcomes: OS-1 and PFS-6. The areas under the ROC curves (AUC) and the associated 95% confidence intervals were estimated empirically. A marker was considered effective in classification of an outcome status when its lower 95% CI of the AUC was at least 0.50. Correlations between parameters were assessed using Pearson correlation coefficients. All analyses were done with SAS 9.4 (Cary, NC, USA).Seventeen participants (11 men, 6 women, median age 59 yrs, range 45-77) from 4 sites had analyzable MRS datasets with uniform parameters at their baseline scan. The OS-1 for the 17 evaluable patients was 59% (10/17) and the PFS-6 was 65% (11/17). ROC analysis found NAA/Cho in tumor (AUC = 0.83, 95% CI: 0.61 to 1.00), and in the peritumoral (AUC = 0.95, 95% CI 0.85 to 1.00) were predictive of survival at 1 year with higher values predicting increased OS-1. Lac/Cr in the tumor was a significant negative predictor of PFS-6 (AUC = 0.79, 95% CI 0.53 to 1.00). NAA/Cho was not effective in predicting PFS-6, nor was Lac/Cr in predicting OS-1. Cho/Cr was effective in neither (Table 1). In addition, we explored the correlation between spectroscopic markers and PET markers of tumor hypoxia as well as MR imaging markers of vascularity including CBV, CBF and Ktrans. None of these markers were correlated with MRS markers, as shown by the Pearson correlation coefficients below 0.43, and not statistically significant (Table 2).Our data suggests MRS markers of tumor burden (NAA/Cho) and tumor hypoxia (Lac/Cr) were significant predictors of survival or progression free survival. Even in the setting of a multi-center trial comprising different vendors, field strengths and varying levels of expertise at data acquisition, those markers predicted OS-1 and PFS-6 well. Peripheral NAA/Cho showed the highest prediction of OS-1, perhaps indicating that increased tumor infiltration into the peritumoral parenchyma reflects tumor growth and subsequently poorer outcomes while tumoral spectra are often already characterized by hypoxia and necrosis. These results emphasize that MRSI (compared to a single voxel approach) is essential in the evaluation of brain tumors. Interestingly no correlation between Lac/Cr and 18F-FMISO SUV, both markers of tumor hypoxia, was observed in this study which could be attributed to a limited sample size of or slightly different voxel sizes. Overall, none of the MR spectroscopic markers strongly correlated with the previously analyzed MRI and PET markers, suggesting that MRS markers may provide complementary information.Standardized MRSI should be considered for incorporation into future multi-center clinical trials and may be useful in diagnosis and in risk stratifying patients.