This story has been updated with additional information on MDxHealth's MGMT glioblastoma test.
CHICAGO – Clinical trials investigating new treatment options for glioblastoma, an aggressive form of brain cancer, often fail to substantially extend the lives of patients, and Roche's latest attempt to test out Avastin (bevacizumab) as a front-line defense for those with this disease also disappointed in this regard.
However, researchers involved in an NCI-funded cooperative group study have developed a multi-gene test that has shown promise in being able to pick out which patients are likely to have better outcomes following treatment with an Avastin-containing regimen. At the American Society of Clinical Oncology's annual meeting this week, researchers conducting RTOG 0825, a study of Avastin in newly diagnosed glioblastoma patients, reported that they had developed a gene expression signature that was able to divide patients into a "favorable group" that is likely to respond to treatment with Avastin and chemoradiation, and an "unfavorable group" that's unlikely to benefit from treatment.
Data from the RTOG 0825 molecular analysis was presented against the backdrop of data released from the Phase III AVAglio study, sponsored by Roche. AVAGlio showed that Avastin significantly improved progression-free survival – the length of time during which patients' disease didn't worsen – in newly diagnosed glioblastoma patients who received the drug in combination with radiotherapy and the chemotherapy temozolomide compared to those who received chemoradiation plus placebo. However, patients in the Avastin arm didn't live significantly longer in AVAglio compared to those in the standard treatment arm.
Roche is discussing the data with regulatory authorities, the company said in a statement. Whether the US Food and Drug Administration will be satisfied with the data from AVAglio as sufficient proof of Avastin's efficacy as a first-line treatment for glioblastoma remains to be seen. In 2009, the FDA granted accelerated approval to Avastin as a second-line treatment for glioblastoma patients who had progressive disease and had received previous treatment. Roche subsidiary Genentech received approval for this indication based on response rates seen in two single-arm studies.
When a drug is approved under an accelerated time frame, the sponsors are required to submit data from more extensive studies on that treatment. AVAglio was part of Roche's commitment to the FDA to study Avastin further in glioblastoma patients.
Because Genentech was unable to show a survival advantage for Avastin as a treatment for metastatic breast cancer, the FDA revoked this indication for the drug in 2011, three years after the agency had granted accelerated approval in this setting (PGx Reporter 11/30/2011). However, glioblastoma is a very different disease than breast cancer, and breast cancer patients have more treatment options than those with this aggressive form of brain cancer.
After diagnosis with glioblastoma, patients live around a year with the help of radiation treatment and temozolomide, which extends their lives for only a few months. Surgery to remove brain tumors doesn't benefit most newly diagnosed glioblastoma patients because the disease spreads quickly. Recurrent disease progresses more slowly, and differs in many ways from the first iteration of the illness. Given the nature of the illness and the limited treatment options, the fact that Avastin failed to significantly impact survival in AVAglio in newly diagnosed glioblastoma patients may not impact the availability of the drug as an option for patients in later stages of the disease.
"Almost everyone with this disease dies from this disease. Unfortunately, no other treatments have shown to be definitively impactful in terms of quality and quantity of life up to this point," Howard Alan Fine of New York University Medical Center said in discussing the data from RTOG 0825 at a plenary session during the meeting.
"For those of us who have been treating these patients for more than two decades from when we first saw the impressive responses in recurrent disease with [Avastin], we were tremendously excited," Fine said. "But I guess those of us who have done trials in this disease for this long, knew that it wasn't going to be that easy."
Toward a predictive test
In the 900-patient AVAglio trial, newly diagnosed glioblastoma patients who received Avastin plus radiotherapy and temozolomide experienced median progression-free survival of 10.6 months versus 6.2 months for those receiving placebo plus chemoradiation. Median overall survival in the Avastin arm and the comparator arm was 16.8 months and 16.7 months, respectively.
At two years follow-up, 34 percent of patients receiving Avastin in AVAglio were alive compared to 30 percent of those receiving chemoradiation. Bleeding in parts of the body (except the brain), high blood pressure, excess protein in urine, and blood clots were some of the adverse events that occurred more frequently in patients in the Avastin arm compared to the comparator arm.
Roche presented data at ASCO from AVAglio in which researchers gauged baseline plasma VEGF-A and VEGFR-2 protein levels in 571 enrolled patients using multiplex ELISA technology. But based on these biomarkers, researchers couldn't identify which patients had statistically significant progression-free survival on Avastin or standard treatment.
Similarly, in RTOG 0825, newly diagnosed glioblastoma patients receiving Avastin and chemoradiation had median progression-free survival of 10.7 months compared to 7.3 months for those on standard treatment, and median overall survival was 15.7 months versus 16.1 months, respectively. None of these primary endpoints met prespecified targets. However, the molecular analysis in this study hit on more promising results.
One of the secondary measures of RTOG 0825 was to look at whether the molecular profile of glioblastoma patients held any clues as to how they would respond to the Avastin regimen. In exploring this, researchers led by Erik Sulman of the University of Texas MD Anderson Cancer Center first tested patients with a previously identified set of nine genes. Seven of these genes were mesenchymal-associated genes, which have been found in studies to be upregulated in glioblastoma patients, involved in cell invasion and angiogenesis and associated with poor patient survival. Two of the genes are known to be involved in neural development and have also been linked to glioblastoma.
This nine-gene prognostic model was able to separate patients in RTOG 0825 into favorable and unfavorable response groups and showed that those in the favorable group had a modest overall survival and progression-free survival benefit compared to the unfavorable group. Based on this hint, Sulman and colleagues conducted gene expression profiling on a subset of participants' samples using the Illumina Whole-Genome DASL assay, performed unbiased gene selection among 43 genes, and developed a 10-gene predictor of treatment response.
According to Sulman, the predictor, dubbed PRoB-GBM, did not contain the same genes as in the first nine-gene test, but contained some "mesenchymal-like genes." Researchers validated this RT-PCR test on a larger cohort of patients in RTOG 0825 and found that the test "clearly separated favorable and unfavorable" groups in terms of progression-free survival and overall survival.
In the validation cohort, median progression-free survival was 13.2 months in the favorable group and 7.2 months in the unfavorable group, and median overall survival was 20.3 months in the favorable group and 10.4 months in the unfavorable group. Sulman pointed out that 70 percent of patients' tumors tested with PRoB-GBM fell into the favorable group, and around 30 percent fell into the unfavorable category.
Among those in the favorable group, patients treated with Avastin and chemoradiation had median progression-free survival of 13.2 months compared to 7.3 months for those in the standard treatment arm. Even with the help of the gene expression test, however, Avastin-treated patients in the favorable group had median overall survival of 20.3 months compared to 17.9 months for those receiving standard treatment. "Admittedly, this did not reach statistical significance," Sulman acknowledged at the meeting.
In the unfavorable group, progression-free survival was similar for both treatment arms, but Avastin-treated patients did "much worse" in terms of overall survival compared to those on standard treatment, Sulman noted. Median overall survival for patients in the unfavorable category receiving Avastin and chemoradiation was 10.4 months versus 15.4 months for those receiving standard treatment.
Some patients in the standard treatment arm, once they progressed, were crossed over to receive Avastin. Researchers tested those patients to see if PRoB-GBM could predict response, but it could not. "At least based on this analysis, this predictor doesn't appear to apply in the setting of recurrent disease," Sulman said.
This analysis ultimately showed that "we have [developed] this molecular diagnostic suitable for FFPE tissue, based on real-time PCR for patients with newly diagnosed glioblastoma who received [Avastin], that predicts an improvement in survival," Sulman said, adding that "clearly, further validation is warranted."
A Genentech spokesperson told PGx Reporter that the firm hasn't taken a close look at the "exploratory" molecular analysis in RTOG 0825. Sulman and colleagues, meanwhile, will continue to examine additional patients in RTOG 0825 using the molecular test. "Ultimately, any predictive biomarker needs to be validated prospectively in a patient selection trial," he noted. "And that will need to be done, but this was an important first step."
The Genentech spokesperson highlighted, however, the Phase II GLARIUS trial in which 71 percent of patients with newly diagnosed glioblastoma, whose tumors had non-methylated MGMT, were progression-free after six months after treatment with an Avastin/irinotecan/radiation regimen compared to 26 percent of those on temozolomide/radiotherapy. "This data suggested that MGMT warrants further study as a potential biomarker for which patients may be appropriate candidates for Avastin use," the spokesperson said.
Importance of molecular testing
"The trials with glioblastoma have had trouble in the past. Identifying rare subgroups with responses that are favorable, or potentially unfavorable groups are both important," Keith Ligon of Dana Farber/Harvard Cancer Center said at ASCO in discussing the molecular analysis done on RTOG 0825. "Unfortunately, we have lots of negative trials [in glioblastoma], and it's even more critical in that situation to apply tools to work the trials out and understand better why the trials failed."
Ligon noted that single-marker tests may have hindered research to identify biomarkers associated with treatment response in glioblastoma, but multiplex tests like PRoB-GBM may speed this process along.
Separately at the meeting, Merck also released data from a failed Phase III trial investigating an integrin inhibitor called cilengitide in newly diagnosed glioblastoma patients whose tumors harbored MGMT gene promoter methylation. Researchers led by Roger Stupp, president-elect of the European Organization for Research and Treatment of Cancer, prospectively tested close to 3.500 patients for methylated MGMT under a collaboration with diagnostics firm MDxHealth. They then randomized 545 patients to receive either cilengitide in combination with temozolomide and radiotherapy or just temozolomide and radiotherapy.
In the study, median overall survival in both arms was 26.3 months, and median progression-free survival in the cilengitide arm was 13.5 months and 10.7 months in the control arm. Upon analyzing additional subgroups in the study, Stupp noted that his team couldn't find a single subset of patients with response that suggested activity with this agent. Study investigators found no new or unexpected safety issues with cilengitide.
Merck conducted this Phase III study after earlier trials in small cohorts of newly diagnosed glioblastoma patients suggested that cilengitide may improve survival in those with methylated MGMT. Based on encouraging early data, Merck announced last year that it would fund the development, regulatory approval, and commercial launch of MDxHealth's test that gauges methylated MGMT as a companion diagnostic for cilengitide (PGx Reporter 7/11/2012).
The MGMT gene is involved in cellular DNA repair, and past studies suggest that patients with methylated MGMT don't express the gene normally, which in turn makes tumor cells more sensitive to standard chemoradiation. Despite the failure of this trial, Merck is also studying cilengitide in newly diagnosed glioblastoma with unmethylated MGMT and in non-small cell lung cancer.
Although MDxHealth's MGMT test will no longer be developed as a companion test for cilengitide, the company has partnerships with a number of drug developers investigating the role of methylated MGMT in various drugs. MDxHealth markets PredictMDx for Glioblastoma as a laboratory test.
Despite the failure of the Phase III trial in methylated MGMT glioblastoma, Stupp highlighted that the study proves it is possible to coordinate prospective, centrally conducted molecular testing for a large number of patients before they are randomized to receive treatment in a global, multi-center trial. "It shows … that you can take, we must take, molecular markers forward, even though we may not have yet found the ultimate molecular marker," Stupp said.