BIOM-27. PROGNOSTIC SIGNIFICANCE OF EXTENT OF RESECTION IN GLIOMA ACCORDING TO THE 2021 WHO CLASSIFICATION

Abstract

Abstract BACKGROUND In the updated 2021 WHO classification, diffuse gliomas were strictly reclassified by molecular statuses. In glioblastoma (GBM), the prognostic significance of the resection has been shown, but the excision rate to be achieved in the new classification has not been defined. Moreover, the correlation between the extent of resection (EOR) and the prognosis is still controversial for other gliomas. METHODS IDH 1/2 mutations and TERT promoter mutations were analyzed by Sanger sequencing, 1p/19q co-deletion by microsatellite or MLPA, and EGFR amplification and CDKN2A deletions by MLPA. The correlation between the resection rate and prognosis of each tumor type in the 2021/2016 WHO classification was analyzed retrospectively. RESULTS According to the 2021 classification, 293 patients with GBM, IDH-wild type, 68 with astrocytoma, IDH-mutant (2/3/4 22/26/20), and 58 with oligodendroglioma, IDH-mutant and 1p/19q co-deleted were identified. Based on the 2016 classification, they were diagnosed as 314 GBM, 106 astrocytoma (Gd II/III 37/69), and 59 oligodendroglioma. For GBM, IDH-wild type (2021 classification), a prolonged OS benefit was observed with >25% removal (p=0.042), whereas, more than 20% of tumor removal for patients with GBM (2016 classification) resulted in OS prolongation. EOR was a significant favorable prognostic factor for grade II/III astrocytoma by the 2016 classification, but not for astrocytoma, IDH-mutant (grade 2/3) in the 2021 classification. When analyzed only in patients with astrocytoma, IDH-mutant by the 2021 classification, EOR was not significantly prognostic, suggesting that poorer prognosis of patients with unresectable IDH-wild type astrocytomas (2016 classification) might have a negative impact on the outcome. CONCLUSION There was a strong correlation between EOR and prognosis in patients with GBM, and >25% removal was considered significant according to the 2021 classification. For astrocytoma in the 2021 classification, EOR did not show a prognostic significance, but further validation including grading effect is warranted.