Association of MGMT status with survival in low and high-grade IDH-mutant astrocytomas.

2065 Background: The role of MGMT promoter methylation status on survival for IDH-mutant astrocytomas is less known than for glioblastoma, IDH-wildtype (GBM). Further, different laboratories utilize a variety of techniques to measure methylation of the MGMT gene promoter region, including pyrosequencing, methylation-specific polymerase chain reaction (PCR), and direct Sanger sequencing; these techniques are limited by low quantitative accuracy, short read length, and low sample throughput. In the current study, we used a large database of next-generation sequencing (NGS) and whole-transcriptome sequencing (WTS) performed in a single laboratory to determine the role of MGMT status on survival in IDH-mutant astrocytomas (CNS WHO grades 2-3 and 4), as well as in GBM. Methods: 10,181 glioma samples were analyzed by NGS (592, NextSeq, or WES, NovaSeq) and WTS (NovaSeq) at Caris Life Sciences (Phoenix, AZ), including determination of methylation status of the MGMT promoter region by pyrosequencing. Real-world overall survival was obtained from insurance claims data and calculated from initial diagnosis to last contact, while TMZ-OS was calculated from first dose of temozolomide to last of treatment. Hazard ratios (HRs) were analyzed using Cox proportional hazards model and p values (log-rank test). Multivariate regression analysis was performed on age, gender, radiation treatment, temozolomide treatment, and mutations in different biomarkers. Fisher’s exact tests was used at a significance level of 0.05. Results: 693 IDH-mutant astrocytomas CNS WHO grades 2 or 3 (“g2/3”), 251 IDH-mutant astrocytoma CNS WHO grade 4 (“g4”), and 4469 glioblastoma (“GBM”) met inclusion criteria. Univariate and multivariate survival analysis showed that MGMT promoter methylation (mMGMT vs. unmethylated, uMGMT) was associated with improved OS only in GBM (HR = 0.62, 95% CI: 0.57 – 0.67, p < 0.0001), but not in astrocytoma-g2/3 and g4. Similarly, TMZ-OS was only significantly longer in mMGMT vs. uMGMT in GBM (HR = 0.53, 95% CI: 0.48 – 0.58, p < 0.0001). In astrocytoma-g2/3, ATRX mutation was more prevalent in mMGMT than uMGMT (73.9% vs. 62.6%, p < 0.05), and SETD2 was more prevalent in uMGMT than mMGMT (4% vs. 1.1%, p < 0.05). Tumor mutational burden (TMB)-high was more prevalent in mMGMT than uMGMT in astrocytoma-g4 (14.8% vs. 2.7%, p < 0.05) and in GBM (5.4% vs. 1.9%, p < 0.0001). In GBM, many genes had different mutational rates between mMGMT and uMGMT groups, including MSH6 (2% vs. 0.7%, p < 0.001), ATRX (3.1% vs. 1.6%, p < 0.01), and CDKN2A (4.3% vs. 2.5%, p < 0.01). Conclusions: mMGMT was not associated with better survival in IDH-mutant astrocytoma-g2/3 or g4with respect to OS or TMZ-OS, whereas mMGMT conferred improved survival in GBM. These results, derived from a large database using same platform (next-generation sequencing at a single laboratory), support similar findings from recent, smaller cohort studies.