NIMG-77. IMPACT OF POST-SURGICAL ENHANCING TUMOR VOLUME AND T2/FLAIR VOLUME ON THE SURVIVAL IMPACT OF BEVACIZUMAB IN NRG ONCOLOGY/RTOG 0825

Abstract

INTRODUCTION: RTOG 0825 randomized 621 newly-diagnosed glioblastoma patients to treatment with or without bevacizumab, in addition to standard-of-care radiotherapy plus concurrent/adjuvant temozolomide. No significant difference was seen between the treatment arms in overall survival (OS), and the difference in progression free survival (PFS) did not meet the pre-defined statistical margin. We evaluated the impact of post-surgical MRI-determined residual tumor on outcomes. METHOD(S): 431 (69.4%) patients had post-operative T1 MRIs (with and without gadolinium) and 517 (83.2%) had T 2 or FLAIR images. Volumetric segmentation was performed to calculate residual enhancing (T1Gd-T1) volume (rEV) and T2/FLAIR volume (rT2FV). Multivariable analyses were performed using Cox models with pretreatment characteristics and treatment as covariates. RESULT(S): Median post-operative, pretreatment rEV was 2.8 cc (range 0.0-79.6 cc) and rT2FV volume was 52.3 cc (0.0-279. 8 cc). Neither age nor MGMT methylation were predictors of rEV or rT2FV. Ninety-four (21.8%) patients had an imaging-complete resection of enhancing tumor (rEV=0.0). We did not detect a significant difference in OS or PFS for an imaging-complete resection. Notably, however, a rEV CONCLUSION(S): These prospective data demonstrate the benefits associated with minimizing residual contrast-enhancing tumor in glioblastoma. MGMT status did not appear to independently determine residual tumor volume after surgery. Finally, bevacizumab appears to provide PFS benefit in patients with smaller rT2FV, and diminishes OS in patients with larger rT2FV.