P01.163 Impact of absolute postoperative tumor volume on survival in glioblastoma and significance of MGMT-methylation status for benefit of increasing surgical resection

Abstract

INTRODUCTION: Previous studies have demonstrated a survival benefit with increasing extent of resection (EOR) for patients with glioblastoma. However, EOR is a relative measurement making it difficult to determine the significance of residual tumor size in clinical practice. Our aim is to determine whether absolute postoperative volume affects survival similarly. Moreover, despite that methylation of the enzyme MGMT is associated with a better prognosis in glioblastoma, it is still unknown whether the survival benefit of increasing surgical resection differs between patients with different MGMT-methylation status. MATERIALS AND METHODS: In total 286 patients with newly diagnosed supratentorial glioblastoma that underwent cytoreductive surgery between 2010 and 2016 were identified in a regional cancer registry. Pre- and postoperative 3D volumetric measurements were performed retrospectively. Information about age at surgery, pre- and postoperative WHO performance status, oncological treatment and histopathological data including result of MGMT-methylation status analysis were collected. RESULTS: The median age of patients was 65 years. The median postoperative volume was 0.513 cm3 and median EOR was 98,7%. Median overall survival time was 13 months and for patients with gross total resection 15.3 months. Age, pre- and postoperative performance status and oncological treatment were included in a multivariate Cox proportional hazards analysis. Postoperative volume and EOR were both predictive of survival at p=0.0090 with a concordance index of 0.71. In a separate multivariate interaction analysis including the 151 patients with known MGMT-methylation status the p-value for interaction between MGMT-methylation and EOR was 0.60 and respectively for postoperative volume 0.54. CONCLUSIONS: Postoperative volume affects survival in patients with newly diagnosed glioblastoma with similar descriptive abilities as EOR. In considering risk of neurological morbidity no significant differences in postoperative performance status were seen between patients with different EOR or postoperative volume. MGMT-methylation status seems to not significantly affect survival in relation to EOR or postoperative volume, although a slight trend was observed towards a greater benefit for patients with methylated MGMT. Further studies will clarify whether MGMT or other molecular pathological properties in glioblastoma affects benefit of EOR.