Tumor perfusion during bevacizumab and irinotecan in recurrent glioblastoma: A multimodal approach.

Abstract

2074 Background: Angiogenesis is a requirement for progression of glioblastoma (GBM) and vascular endothelial growth factor (VEGF) is a mediator of neo-angiogenesis in this tumor. Bevacizumab (Bev), an antibody directed to VEGF, was recently used to treat GBM. However in vivo modifications induced by treatment are still not clearly understood. Aim of this study is to analyze tumor changes induced by Irinotecan (Ir) and Bev, using two different methodologies: relative CBV variation (rCBV) and Difference Perfusion Maps (DPMs). Methods: 42 recurrent GBM patients underwent Bev (10 mg/kg) and Ir (125 or 340 mg/m2) treatment every 2 weeks and were followed up with a radiological protocol, including Dynamic Susceptibility Contrast MRI every 8 weeks. Radiological responses were assessed based on RANO criteria (Wen et al, 2012). Two methods were used to assess perfusion changes. In method A, relative CBV variation after 8 weeks of treatment was calculated through semi-automatic ROI placement in the same anatomic region as in baseline. In method B, relative CBV variations with respect to baseline values were calculated into the evolving tumour region by means of a voxel-by-voxel difference. DPMs were created showing where rCBV significantly increased, decreased or remained unchanged. Results: After a median follow-up of 33.5 months median overall survival (OS) was 35.0 weeks and median progression free survival (PFS) was 20.0 weeks. Method A showed a significant decrease of rCBV for patients with stable disease or partial response after 8 weeks of treatment (p = 0.01) while progressing patients maintained elevated levels of rCBV (p = 0.38). Method B, based on DPMs, showed that patients presenting rCBV increase higher than 25° percentile (corresponding to rCBV increase higher than 18% of tumor volume) had a significantly longer PFS (p = 0.045) and OS (p = 0.016). Conclusions: Using DPM we observed that early increase in global perfusion is related to better survival. This may suggest that Bev, when effective, reduces blood-brain barrier permeability with a higher contrast retention in vessels. If confirmed by further studies this measure could be useful in identifying responders to Bev.