Radiographic evaluation of recurrent glioblastoma multiforme (GBM) in patients treated with bevacizumab and irinotecan

Abstract

12512 Background: Recurrent GBM carries a poor prognosis after first-line therapies have been exhausted, even in the setting of gross total resection. Bevacizumab and Irinotecan have shown promising results in patients with recurrent GBM (Stark-Vance, et al. Neuro- Oncol, 2005). We sought to retrospectively document the short-term effects of this chemotherapeutic regimen on recurrent GBM, as evidenced by comparative MRI brain scans obtained prior to, and one-month following initiation of treatment. Methods: We collected brain MRI data from August 2005 to December 2006, in which post-contrast spin-echo T1-weighted images demonstrated measurable enhancement and/or GBM tumor mass. Having failed temozolomide and radiation therapy, 14 consecutive patients’ MRI scans were available for review at this institution by a neuro-radiologist, in which both pre- and post-treatment hard and/or soft copy MR images were available for direct measurement. Each was treated with Bevacizumab 5 mg/kg IV and Irinotecan 125 mg/m2 IV infusion every 2 weeks until disease progression, or development of unacceptable toxicity. We measured pre- and post-treatment recurrent GBM bulk tumor in anteroposterior, transverse, and cranio-caudad dimensions, and calculated volumetric data, assuming an ellipsoid tumor configuration. Results: Pre-treatment MRI scans were performed 2 weeks prior to initiation of therapy (Mean: 13 days; Median: 10 days). Post-treatment scans were performed at approximately one month following initial treatment (Mean: 30 days; Median: 28 days). All patients witnessed significant decrease in tumor bulk volume ranging from 15.3 to 89.8%, having received an average of two cycles of chemotherapy. We observed a mean decrease in tumor volume of 46.6% (SD = 22.6%; SEM = 6.0%; 95% CI = 33.6 - 60.0 % decrease). Conclusions: We report 46.6% mean reduction in recurrent GBM tumor bulk at an average of 1-month post-treatment in patients treated with an average of two cycles of Bevacizumab and Irinotecan therapy. These promising initial results necessitate further long-term prospective evaluation of this chemotherapy. No significant financial relationships to disclose.