Six out of 24 patients with measurable disease experienced any tumor shrinkage. Assessments of response were conducted by study investigators according to RANO criteria. Cases with greater than a 25% reduction in area of measurable disease were also reviewed by an expert panel blinded to treatment assignment. Per the investigator review, 4 patients experienced significant tumor shrinkage; however, two of these were deemed protocol violations because while the patient had prior bevacizumab exposure, they did not meet the strict definition of bevacizumab refractory as outlined in the ReACT protocol. 32% of patients had stable disease or better for greater than 2 months. 

Preliminary Analysis of Objective Response Bevacizumab-Refractory Recurrent GBM
Patient Investigator Assessment Expert Panel Review
1 PR (79% shrinkage) SD*
2 90% shrinkage; not sustained SD*
Patients with progression > 2 months after discontinuation of bevacizumab:
3 CR (9.3 months duration) SD*
4 100% shrinkage; not sustained PR
*Enhancement judged not measureable, but thought to improve on treatment

Immune Response Overview

Remarkably robust humoral responses comparable or exceeding those seen in the frontline setting (ACT III) were observed despite advanced disease, use of steroids, prior chemotherapy exposure and the presence of bulky tumor. There was a four-fold increase in anti-EGFRvIII antibody titers in 84% of bevacizumab-naïve patients and 79% of bevacizumab-refractory patients. A high-titer response was noted (range of 1:12,800 to 1:6,553,600) in 50% of bevacizumab-naïve patients and 67% of bevacizumab-refractory patients and titers increased with time on study. Importantly, the study suggests that early development of anti-EGFRvIII titer may be predictive of improved outcomes in this patient population as improved survival was associated with rapid generation of humoral response. These results also provide further support for the rindopepimut/bevacizumab combination approach, as prior studies have suggested that bevacizumab can enhance immune-mediated anti-tumor effects in tumor model and may, in turn, optimize EGFRvIII specific immune response. 

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