Part of the problem is that the body's immune system recognizes tumors not as a foreign threat, but as a familiar body tissue. Lotze noted that tumors grow for up to 10 years before they reach a size that can be detected by doctors.
In that time, they have become used to the body's immune responses. That makes it doubly hard for a vaccine to prompt the immune system to attack tumor cells.
"The whole field has been sobered by the slow progress that has been occurring over the last 20 years," Lotze said. "But we've seen substantial evidence in recent years that suggests that we're on the right track."
Dr. Hideho Okada, co-leader of the Brain Tumor Program at the University of Pittsburgh Cancer Institute, said using personalized medicine like the brain cancer vaccine offers a big advantage. A vaccine for melanoma used the same approach, but, like a majority of other cancer vaccines so far, failed in early trials.
"That doesn't necessarily mean it wouldn't work for brain cancer," Okada said.
Parsa said randomized controlled trials for the brain cancer vaccine will begin in the next six months.
"We have a very good indication that it will work," Parsa said. "But we don't definitively know how this vaccine will do."