SURG-16PROGNOSTIC VALUE OF THE EXTENT OF RESECTION AND IDH1 MUTATION STATUS IN WHO GRADE II ASTROCYTOMAS

Abstract

INTRODUCTION: Current evidence supports a maximized extent of resection (EOR) in low-grade gliomas (LGG). However, conclusions were drawn in negligence of different histologic subtypes, underrating the fact that histology and molecular markers, like IDH1, per se confer divergent outcomes. We therefore evaluated the prognostic impact of extensive surgery in pure astrocytic LGGs stratified for IDH1. METHODS: From a consecutive series of 179 LGGs treated since 2004, we analyzed 46 pure astrocytomas with open tumor resection at 1st diagnosis. IDH1 mutation status was available for all patients. Pre-, early postoperative and follow-up tumor volumes were obtained from FLAIR images. Subgroup analysis for EOR ≥40% (n = 39) was performed. Analysis for overall (OS), progression-free (PFS), malignant progression-free survival (MPFS) and time to re-intervention (TTR) was conducted with uni- (uv) and multivariate (mv) regression models. RESULTS: A median final EOR of 90.4% (range 17.5 - 100%) was achieved at follow-up MRI, leaving a median residual tumor volume of 4.09cm3. EOR did not impact on OS but was significantly associated with PFS (HR 0.23; p = 0.04; uv) and TTR (HR = 0.23; p = 0.04; uv). IDH1 was the only independent prognosticator for OS (HR 0.04; p = 0.002; mv). After stratification for EOR ≥40%, initial and residual tumor volumes were both predictive of OS (HR >1, p < 0.01 and p < 0.05, respectively, uv), even after adjustment for IDH1. Significant associations of residual tumor with survival endpoints were exclusively found on follow-up but not on early postoperative MRI. CONCLUSION: After stratification for histology and IDH1, greater EOR delayed tumor progression and time to re-intervention. IDH1 was the strongest predictor of OS, potentially obscuring benefits of surgery. Our approach illustrates the diverse impact of biological and surgical factors upon outcome and highlights critical differences in prognostic value between early and late postoperative imaging. The need to strive for maximized resections in low-grade astrocytomas is underscored.