IMG-145. Evaluation of pMGMT Methylation Status on Radiographic Presentation in Glioblastoma

PURPOSE Prior glioblastoma (GBM) studies have investigated prognostic factors for longer overall survival (OS), including MGMT promoter (pMGMT) methylation. However, the association between pMGMT methylation status and radiographic factors in GBM is not well understood. To study this, we created a database of pathology-confirmed GBM patients (with clinical, pathology, and radiographic data) at a large tertiary care center. Materials and METHODS 279 patients with pathology-proven GBM and known pMGMT methylation status were identified. Confounding factors including age, sex, tumor size, and lobe involvement were abstracted. Chi-squared analysis and logistic regression were performed to assess the association between pMGMT methylation status and radiographic features and 36-month OS rate (OS36). RESULTS Radiographic GBM tumor location in pMGMT-methylated cases (118) vs. pMGMT-unmethylated cases (161) was 46.6% vs. 48.7% frontal (p=0.81), 47.4% vs. 34.2% parietal (p= 0.037), 46.6% vs. 52.5% temporal (p=0.39), and 17.2% vs. 21.5% occipital (p=0.47) lobes, and 18.2% vs. 26.5% for bilateral involvement (p=0.14). Male gender was significantly more common in pMGMT-unmethylated GBMs (67.7%) than pMGMT-methylated (49.1%, p=0.003). Overall survival was significantly longer among all cases of pMGMT methylated (694.61 days) vs. unmethylated GBMs (388.66 days) (p<0.01). Subgroup analysis showed a significant difference in mOS of pMGMT-methylated (637.74 days) vs. pMGMT-unmethylated cases (375.89 days) in the temporal lobe (p<0.01). Among all tumor locations, univariate analysis revealed that pMGMT-methylation vs. non-methylation was associated with a significantly higher OS36 (16.1% vs. 3.9%, p<0.001); on multivariate analysis involving the confounding factors, the p-value remained statistically significant (p=0.017). CONCLUSION Compared to pMGMT-unmethylated status, pMGMT-methylation was significantly more common in the parietal lobe and less common in male GBM patients. Subgroup analysis revealed significantly longer mOS in pMGMT-methylated vs. pMGMT-unmethylated cases with temporal lobe involvement. Accounting for the confounding factors via multivariate analysis, the presence of pMGMT methylation remained associated with a significantly higher OS36 among all cases.