Another possibility to account for the worsening neurocognitive function with bevacizumab is the drug’s documented ability to stabilize the blood-brain barrier and decrease MRI gadolinium enhancement, he said. This could mean that patients experience radiographic occult disease progression that does not show up well on brain scans.
Dr. Gilbert and Dr. Fine commented that theoretically at least, glioblastoma should be an ideal target for angiogenesis inhibitors such as bevacizumab, because they display a high degree of vascularity, and endothelial proliferation is part of the pathologic definition of the disease.
But although bevacizumab has been demonstrated to improve response rates and delay progression in recurrent glioblastoma, its relative lack of efficacy in the first line is puzzling, Dr. Fine said.
Potential explanations include the crossover designs of both the RTOG and Avaglio studies, suboptimal delivery of bevacizumab to the tumor, or the possibility that the vascular endothelial growth factor receptor may not be the best target in glioblastoma.
"Despite these new data demonstrating its limitation, I feel very strongly that bevacizumab represents the single most important agent in glioblastoma since temozolomide, and maybe even more so. Ongoing and future trials will better define how and when it should be optimally used in these patients that have such limited therapeutic options," Dr. Fine concluded.
The RTOG 0285 study was supported by the National Cancer Institute, with additional support from Genentech. Avaglio was supported by Roche. Dr. Gilbert disclosed consulting for, and receiving honoraria and research support from, Genentech. Dr. Mason disclosed being a consultant/adviser to Hoffman-La Roche. Dr. Fine reported having no relevant financial disclosures.