INNV-11. Single institution retrospective study determining characteristics of non-enhancing glioblastoma

Abstract BACKGROUND Glioblastomas are contrast enhancing tumors with perilesional edema. On the other hand, IDH mutant/low grade gliomas are non-contrast enhancing tumors. A small percentage of glioblastomas present as non-enhancing lesions. Molecular characteristics and behavior of non-enhancing glioblastoma is not well defined. METHODS We conducted a retrospective analysis at our institution from 2020 to 2024 to define occurrence, pathologic features, molecular characteristics, and outcomes of non-enhancing glioblastoma. RESULTS Of 100 glioblastoma patients treated at our institute from 2020 to 2024, 8% had non-enhancing glioblastoma at presentation. All patients are female with median age of 64 (Range 36-84). Four patients (50%) were MGMT methylated and four patients (50%) were MGMT unmethylated. 2 patients (25%) had multifocal disease at presentation; both these patients had MGMT methylated glioblastoma. 3 patients (37.5%) had low Ki-67 labeling index and 50% patients had SETD2 mutation. For unmethylated glioblastoma patients who received standard of care, non-enhancing tumors had a better survival and prolonged time to first progression as compared to enhancing tumors. CONCLUSIONS Current practice for a newly diagnosed non-enhancing tumor (low-grade glioma) is elective (non-urgent) surgical resection or biopsy if surgically accessible versus observation if the tumor surgically inaccessible or in an eloquent location. Our study highlights the importance of close follow up for newly diagnosed non-enhancing glioma to prevent misdiagnosis of glioblastoma. This could be accomplished by scheduling surgical planning scans (functional MRI, MR spectroscopy 4 weeks after the first MRI brain that revealed a non-enhancing glioma. Expedited resection or biopsy should be considered if the tumor shows change in radiographic characteristics like new contrast enhancement, increase in size or perilesional edema. Outcomes of non-enhancing unmethylated glioblastoma treated with standard of care are better than enhancing glioblastoma.