P12.57.B SIGNIFICANCE OF HISTOLOGICAL GRADE IN IDH-MUTANT GLIOMAS: A RETROSPECTIVE COHORT STUDY

Abstract BACKGROUND There are a wide range of outcomes for patients with IDH-mutant gliomas. With the rise of molecular classification, the traditional role of patient stratification by histological grading is less clear. This study aims to evaluate whether WHO grade influences survival outcomes in IDH-mutant gliomas MATERIAL AND METHODS We conducted a retrospective cohort study of patients with IDH-mutant WHO grade 2 and 3 gliomas that were seen at our institution from 2013 to 2024. Clinical, radiographic, and survival data were collected. Overall survival (OS) and progression-free survival (PFS) were defined from the date of first surgical intervention. Kaplan-Meier curves were generated, and survival distributions compared using the log-rank test. Multivariate logistic regression was performed. Statistical analysis was done using SPSS version 29. RESULTS A total of 146 patients were included: 96 with IDH-mutant astrocytomas (Grade 2: n = 53; Grade 3: n = 41) and 52 with IDH-mutant oligodendrogliomas (Grade 2: n = 29; Grade 3: n = 23). The cohort included 88 males and 58 females, with a median age of 49.2 years (range: 23.9-82.1). Disease progression and mortality occurred in 55 and 49 patients, respectively. 104 patients underwent radiotherapy, and 105 received chemotherapy. Overall, patients with Grade 2 tumors had significantly longer survival than those with Grade 3 tumors (median OS: 17.37 years, 95% CI: not estimable vs. 12.24 years, 95% CI: 8.76-15.73; p < 0.001). Among astrocytomas, Grade 2 tumors were also associated with significantly longer OS compared to Grade 3 tumors (median OS: 17.37 years, 95% CI: 7.00-27.75 vs. 8.93 years, 95% CI: 4.56-13.29; p = 0.012). However, progression-free survival (PFS) did not differ significantly between grades (p = 0.515). In oligodendrogliomas, patients with Grade 2 tumors also demonstrated longer OS than those with Grade 3 tumors (2 vs. 6 deaths), although median OS could not be calculated due to limited events. PFS likewise showed no significant difference between grades (p = 0.255). On multivariate logistic regression adjusting for patient, tumor, and treatment variables, Grade 3 tumors (OR = 4.32, 95% CI: 1.76-10.63; p = 0.001) and astrocytoma diagnosis (OR = 6.54, 95% CI: 2.20-19.51; p < 0.001) were the only independent predictors of survival. CONCLUSION Even with molecular classification of IDH-mutant gliomas, histologic grade remains a meaningful prognostic factor for survival. Continuing to develop molecular subtyping into the integrated diagnosis will further help stratify patients and guide treatment decisions.