A bold experiment to kill a vicious form of brain cancer has been granted breakthrough status by the Food and Drug Administration. Results in the earliest stage of testing have been so remarkable, the FDA wants to fast track the treatment to speed it to market.

The therapy uses the polio virus to attack glioblastoma. "60 Minutes" has been following patients in the clinical trial for the last two years.

Stephanie Lipscomb

One of those patients was Stephanie Lipscomb. In 2011, Lipscomb was a 20-year-old nursing student with headaches. A doctor told her she had a glioblastoma tumor the size of a tennis ball and that she had months to live.

She had 98 percent of the tumor removed. Then in 2012, the doctors told her the cancer had come back.

With recurrent glioblastoma, there were no options except the one that had never been tried. Lipscomb became the first volunteer for Duke University's experiment with the polio virus.

The virus is the creation of -- or, the obsession of -- molecular biologist Matthias Gromeier.

Gromeier re-engineered the virus, removing a key genetic sequence. The virus can't survive this way, so he repaired the damage with a harmless bit of cold virus. This new modified polio virus can't cause paralysis or death because it can't reproduce in normal cells.

But it can reproduce in cancer cells, and in the process of replicating, it releases toxins that poison the cell. This process also awakens the immune system to the cancer it never noticed before.

"Why didn't the immune system react to the cancer to begin with," CBS News' Scott Pelley asked Gromeier.

"All human cancers, they develop a shield or shroud of protective measures that make them invisible to the immune system," Gromeier explained. "This is precisely what we try to reverse with our virus. So by infecting the tumor, we are actually removing this protective shield. And enabling the immune system to come in and attack."

It appears the polio starts the killing, but the immune system does most of the damage. Stephanie Lipscomb's tumor shrank for 21 months until it was gone. Three years after the infusion, something unimaginable had happened.

An MRI in August of 2014 showed no active cancer cells at all.

Scott Pelley will have more on Duke University's breakthrough trial, Sunday on "60 Minutes."