July 18, 2013 -- Stephanie Lipscomb, 22, used to have a cancerous tumor the size of a lime in her brain. Monday, she learned that it's the size of a pea, and it's still shrinking even though she hasn't had any chemotherapy or radiation in more than a year.

Doctors at Duke University Medical Center attribute the shrinkage to the modified polio virus they injected into her tumor in May 2012, causing it to shrink without damaging surrounding healthy brain cells.

"Throughout this whole process, I never thought I was going to die," she said, adding that she's a religious person. "This is just another part of my story."

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Lipscomb was finishing up her freshman year at the University of South Carolina Upstate in 2010 when headaches began to plague her as she juggled nursing classes and waitressing. At first, doctors told her she had chronic migraines and gave her caffeine pills. Later, they said she had a sinus infection and gave her antibiotics.

Nothing worked.

"I was pitiful," she said. "By that point, my migraines were so bad, I couldn't eat anything without throwing it back up. I couldn't bathe myself. I couldn't dress myself."

So she called her grandparents, who were nearby. They took her to the emergency room, fearing meningitis.

When Lipscomb's CT brain scans came back, they found a tumor the size of a tennis ball behind her right eye. It was a glioblastoma – the most aggressive kind of brain cancer. She was only 20 years old and told she would live five more years at best.

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The typical glioblastoma patient has between 14 and 18 months to live from the time he or she is diagnosed, said Dr. Annick Desjardins, Lipscomb's neuro-oncologist at the Preston Robert Tisch Brain Tumor Center at Duke University Medical Center. Even after surgery, these types of tumors usually return, signaling that the patient will die in three to eight months.

So when Lipscomb's tumor returned two years after her initial surgery to remove it, Desjardins gave her the option of enrolling in a clinical trial that would use the polio virus's scariest feature: it's ability to unlock a cell, enter it and kill it.

Not all brain cancer patients were eligible, Desjardins said. Lipscomb's tumor was in the right frontal lobe, the area of the brain the controls planning and social skills. Had it been in the area that controls motor skills, vision or language, doctors wouldn't have offered the treatment because it would have been too dangerous to tamper with those areas of the brain.

Lipscomb's mom was on the fence about using the virus.

"She was like, 'What? They're gonna put polio in my daughter? What the heck are they thinking?'" Lipscomb said. "I had to break it down a little more for my mom since I'm a nursing major."

Using polio to treat cancer has been Duke neurosurgeon Dr. Mattias Gromeier's goal for two decades, during which he created and studied a modified version of the virus under a microscope and in monkeys.

Lipscomb became Gromeier's first human patient, and so far, she has survived longer than she would have with standard treatment, Desjardins said.

"It has been most gratifying," Gromeier said.

The standard polio virus uses a receptor molecule present on brain cells to "unlock" them. The virus then enters the cell and replicates until the cell dies. Gromeier's modified version of polio is spliced with a rhinovirus, which causes the common cold. This allows it to enter healthy brain cells using the same receptor molecule – which is also found in most cancers – but the virus is unable to replicate, so it can't hurt the cells.

However, because cancer cells have a different biochemical makeup than regular brain cells, the modified virus is able to enter them, replicate and kill them much like normal polio does. As such, the virus leaves healthy brain tissue unharmed, but it targets and destroys cancer.

Once Lipscomb and her mom were on board, doctors used a catheter to enter Lipscomb's brain and slowly inject the virus over six and a half hours.

It took several months for the virus to start killing Lipscomb's cancer cells, but on Monday, she learned that the tumor was only the size of a pea. Desjardins told her it could come back, but the tumor was still shrinking.

"It was probably one of the most exciting scans I have ever seen of my brain," Lipscomb said. "I don't think it's going to come back."

Of the eight patients treated with the modified polio virus, two have not responded well. Three patients have been improving over the last few months and it is too soon to tell how well three other patients will respond, Gromeier said. He does not know why the tumors didn't shrink in two of the patients.

Another clinical trial is in the works so Gromeier can continue his research.

Since even non-glioblastoma cancer cells have the receptor polio needs to unlock it, Gromeier has been able to shrink melanoma, prostate, colorectal and pancreas cancers in a lab. Still, he has yet to do trials on animals or humans.