INNV-04. SINGLE INSTITUTION RETROSPECTIVE STUDY TO DETERMINE TIME TO FIRST PROGRESSION IN MGMT METHYLATED GLIOBLASTOMA PATIENTS WHO RECEIVED STANDARD OF CARE

Abstract MGMT methylated glioblastomas respond well to standard of care with temozolomide, have a longer survival as well as increased risk of pseudo-progression as compared to unmethylated patients. Shorter survival in these patients despite effective treatments is due to misdiagnosis of true progression (in cases with pseudo-progression) that leads to overtreatment or discontinuation of effective treatments. There are limited non-invasive diagnostic tools to distinguish true progression from pseudo-progression. Knowing the expected time to first true progression will aid with interpretation of MRI changes and serve as an additional tool to distinguish true from pseudo-progression. OBJECTIVE We sought to define the time to first progression in MGMT methylated glioblastoma patients who were treated with standard of care/Stupp protocol (this has not been previously defined). METHODS We conducted a retrospective analysis of an IRB-approved database at our institution from 2019 to 2022 of all MGMT methylated glioblastoma patients who completed Stupp protocol. Time to first progression (time from initial surgery to first true progression) was determined by treating multidisciplinary team based on radiographic review +/- pathology. Eligible MGMT methylated glioblastoma patients had IDH status determined by NGS and completed standard Stupp protocol after surgery. RESULTS Approximately 30% (27) patients with IDH wild-type glioblastoma were MGMT methylated. 10 patients met eligibility criteria. 50% of MGMT methylated GBM patients had multifocal disease at presentation. Median time to first progression in MGMT methylated GBM who received standard of care was 28 months. 20% patients have not had first progression 3 years after initial surgery. CONCLUSION MRI changes on surveillance scans should be carefully interpreted in the first 28 months. Knowing time to first true progression will aid with management decisions and decrease unnecessary early aggressive interventions in MGMT methylated glioblastoma patients. We will validate these findings in a larger patient population at our institution.