EPCO-24. DNA METHYLATION-BASED SUBCLASS PREDICTS THE EFFECT OF THE EXTENT OF RESECTION ON SURVIVAL IN IDH-WILDTYPE GLIOBLASTOMA

Abstract

Abstract BACKGROUND DNA methylation-based classification of diffuse glioma is increasingly used in daily practice. Yet, little is known regarding the prognostic and predictive value of DNA methylation-based subclasses of IDH-wildtype glioblastoma. A recent study found a predictive value for the effect of extent or resection (EOR) on survival for DNA methylation-based subclasses using the v11.4 classifier. We set out to validate these findings in an independent cohort and to test if these results are similar using a more recent version (v12.5) of the classifier. METHODS This concerns a single-center retrospective cohort study of all patients with a glioblastoma, IDH-wildtype of whom DNA methylation was obtained. Patient and tumor characteristics, pre-operative Karnofsky performance status and EOR (complete, subtotal, partial, biopsy) were retrieved. DNA methylation-based classification and MGMT-promoter status were obtained using version 11.4 and 12.5 of the Heidelberg classifier. Progression-free survival (PFS) and overall survival (OS) were collected and validated using the national brain tumor registry. RESULTS Of 149 patients, the subtype was Mesenchymal in 57 (38%), RTK1 in 41 (28%), and RTK2 in 51 patients (34%). PFS and OS did not differ between the three subclasses, also not after pooling RTK1 and RTK2 into one Classical subclass. Complete or subtotal resection resulted in a longer OS than partial resection or biopsy in the entire cohort. This was similar for the pooled Classical subclass. In the Mesenchymal subclass, however, there was no survival advantage for complete or subtotal resection over partial resection or biopsy. These results were similar with the 11.4 and 12.5 classifier version. CONCLUSION In IDH-wildtype glioblastoma of the Mesenchymal subclass complete or subtotal resection does not result in a survival benefit. Our findings evoke the need for pre- or intraoperative assessment of the DNA-methylation based subclass of IDH-wildtype glioblastoma.