Poliovirus treatment for glioblastoma posts 'encouraging' survival data, but work remains

Duke University's poliovirus-based glioblastoma treatment burst on the scene in 2015, thanks to the CBS show "60 Minutes." At the time, only a few patients had received the treatment, and it was unclear if a virus would even work against brain tumors. Now, the scientists behind it are reporting an "encouraging" long-term survival rate in patients with recurrent glioblastoma.

The treatment is a form of the poliovirus vaccine, genetically engineered to preferentially hunt down tumor cells. It is delivered straight into the brain tumor via a surgically implanted catheter. It works by killing cancer cells and simultaneously triggering an immune response against the tumor. Some of the study's authors are named on patents for the technology, which was licensed to Istari Oncology, a Duke spinoff that's working to commercialize the modified virus, known as PVSRIPO.

In a 61-patient, phase 1 trial, patients had a two-year survival rate of 21%, compared to 14% in a historical control group. The contrast in three-year survival was even starker, with 21% of the poliovirus patients and only 4% of the control patients still living. The five-year survival rate for glioblastoma, the most aggressive brain cancer, ranges from 5% to 19%, declining as patients get older.

But the study, published in The New England Journal of Medicine, should be taken with a grain of salt. For starters, it did not have a true control group because of ethical concerns (PDF) behind giving patients a sham treatment. Instead, the researchers used historical data from 104 recurrent glioblastoma patients at Duke who had undergone the standard treatment and who would have been eligible for the trial. Furthermore, the number of patients who survived may be too small to be able to draw concrete conclusions.

The researchers are "encouraged and eager" to press on with further studies, said senior author Darell Bigner, M.D., Ph.D., emeritus director of the Preston Robert Tisch Brain Tumor Center at Duke, in a press release.

“Similar to many immunotherapies, it appears that some patients don’t respond for one reason or another, but if they respond, they often become long-term survivors,” said co-lead author Annick Desjardins, M.D. “The big question is, how can we make sure that everybody responds?”

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There is one cancer-killing virus on the market—Amgen's Imlygic, based on the herpes virus, to treat melanoma—and several more in the clinic. Oncology researchers are particularly interested in testing the viruses along with other cancer treatments, including immune-boosting checkpoint inhibitors. For example, scientists in Canada are testing the Maraba virus with a checkpoint inhibitor in triple-negative breast cancer, and a team in the U.K. is looking at the potential of combining reovirus with radiation, chemotherapy and surgery in brain tumors.

The Duke team is testing the polio-based treatment in combination with approved cancer therapies. PVSRIPO is in a phase 2 trial alongside lomustine, a chemo drug already used in patients with recurrent glioblastoma. And, looking beyond brain cancer, Duke researchers reported during the recent annual meeting of the American Society of Clinical Oncology that a combo of PVSRIPO and a checkpoint inhibitor slowed breast tumor growth in mice.

Some patients with breast cancer or melanoma "will soon be eligible" to join clinical trials testing the poliovirus treatment, Duke said in the statement.