(ABC News) -- Heather Knies was given a death sentence at the age of 24. She battled not one, but two brain tumors -- one of them a grade 4 glioblastoma, the same kind of cancer that killed Sen. Edward Kennedy in 2010.
But today, six years later, she is cancer-free, and her doctors at the Barrow Neurological Institute in Arizona cannot explain it. Her latest MRI is clean, and she is neurologically intact.
The now-32-year-old Knies has not only outlived her life expectancy, she has married and become a mother. Her successful parenthood is remarkable, as intense radiation and chemotherapy can render cancer patients infertile.
Knies's daughter, Zoe, who is 7 months old, celebrated her first Christmas in December.
Knies's doctors say that in rare instances, a patient can break the "biological rules." But most often in those cases, the initial pathology of the tumor was suspect.
In her case, the pathology was "not controversial," according to her surgeon, Dr. Robert Spetzler, director of the Barrow Neurological Institute at Joseph's Hospital and Medical Center in Phoenix.
In his 35 years as a neurosurgeon in the United States, Spetzler said he has never seen such a triumph against a stage 4 glioblastoma.
"It's one of the most malignant tumors there is," he said. "Invariably it will come back and pop up somewhere else in the brain and it's uniformly fatal."
"It's not unheard of that that a few survive -- it's a bell curve and there are outliers," he said. "But in her case, not only has she survived, but she is perfectly normal and there is absolutely no evidence of a tumor on her MRI scan."
Knies has a few of her own theories for why she is still alive today.
"One, being God had a plan for me," said Knies. "I also had a great team of doctors and wonderful family and friends with a positive attitude."
"The mind is so much more powerful than anyone can imagine," she said. "People believe that when they get cancer, it will kill them. But I never once thought that."
Spetzler said Knies was "on the young side" for a glioblastoma, but it can occur at any age, "even in infants."
It all began in 2005, when Knies had the first symptom that something was wrong. She had just started a new job as a receptionist at a doctor's office and was driving home from work.
"Suddenly, I didn't understand what the dashed white line meant in the road," said Knies. "I had been driving since I was 15, so I started panicking and called my Mom. She asked, 'Did you take something?'"
Knies could see, but couldn't understand what she was seeing.
"I was only 24 and I was having visual problems," she said. "I can't even describe them."
Her boss, a dermatologist, insisted she see a specialist, and an MRI showed a low-grade tumor that was pressing on the visual reception cord in her brain.
"I had just moved to Phoenix from Missouri. I was just out of college and felt like I had the whole world waiting there for me," said Knies, ever the optimist. "Looking back, it probably grounded me a bit."
She underwent surgery at another institution, and she enrolled in a drug trial for an oral chemotherapy at Duke University, repeating MRIs every three months.
She says doctors told her to, "Go live your life."
But in less than a year one of the scans showed the white flairs of tumor growth.
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