PATH-44. CLINICAL AND RADIOGRAPHIC PREDICTORS OF PROGNOSIS IN ASTROCYTOMA, IDH-MUTANT, WHO GRADE 4

Abstract BACKGROUND Astrocytoma, IDH-mutant, WHO grade 4, are classified as a separate entity in the 2021 WHO classification of central nervous system tumors and have been poorly characterized in the literature. In this study, we report on the clinical outcomes in a large cohort of newly diagnosed grade 4 IDH-mutant astrocytoma. METHODS We retrospectively identified adult patients with astrocytoma, IDH-mutant, WHO grade 4, treated for their initial diagnosis at Dana-Farber Cancer Institute and Massachusetts General Hospital between 2010 and 2021. Clinical, molecular, and radiological characteristics were recorded, and their association with overall survival (OS) and progression-free survival (PFS) was measured by a log-rank test. If a proportional hazard assumption was violated, we compared the median OS and PFS between groups by the bootstrap method instead. RESULTS We identified 140 patients, with a median age at diagnosis of 37.9 years (range: 19-87) and male predominance (60.7%). MGMT promoter was methylated in 51.4%, and CDKN2A/B homozygous deletion was present in 40 cases (28.6%). Most tumors showed enhancement on the preoperative scan (n=108; 77.1%). Seventy percent of patients had subtotal resection, 25.7% had a gross total resection, and 4.3% had a biopsy. Most patients received standard chemoradiation followed by adjuvant temozolomide (n=103; 73.6%). The median OS was 6.9 years (95% CI: 4.5-9.2), and the median PFS was 3.3 years (95% CI: 2.1-4.4). OS and PFS were not associated with MGMT promoter methylation or the presence of enhancement on the preoperative scan. CDKN2A/B homozygous deletion was associated with worse OS (5.5 vs. 7.8 years, log-rank test-based p-value=0.036) but had no association with PFS (3.4 vs 2.6 years, bootstrap method-based p-value=0.488). CONCLUSIONS In our cohort of astrocytoma, IDH-mutant, WHO Grade 4, CDKN2A/B homozygous deletion had a negative prognostic impact, whereas MGMT promoter methylation status and enhancement on the preoperative scan did not affect survival outcomes.