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Researchers who have harnessed the body’s immune system to fight cancer have found a way to make the approach work even better, using an ordinary tetanus vaccine.

They used their double-vaccine approach to greatly lengthen the lives of patients with one of the deadliest types of cancer — the brain tumor glioblastoma.

“Patients with glioblastoma usually survive for little more than one year. However, in patients who received the immunotherapy, half lived nearly five years or longer from their diagnosis,” said Dr. John Sampson of Duke University Medical Center, who oversaw the study.

The team has been using what is known as immunotherapy to fight glioblastoma. They remove some of the patient’s own immune cells, train them to recognize the tumor, and then re-inject them. It’s a hit-and-miss approach being used against a range of cancers.

With glioblastoma’s there’s a trick — the tumors collect large amounts of a virus called cytomegalovirus or CMV that infects many people, usually without causing symptoms.

“It's the same tetanus booster you get when you step on a rusty nail and have to go into the ER and get a shot."

It’s not clear if CMV actually causes the cancer, but an anti-tumor vaccine that targets CMV sends immune cells right to the brain tumor. This treatment alone has helped patients live longer — from an average of 12 to 14 months for patients who get chemotherapy alone, to more than 18 months with the immunotherapy.

That’s not long enough, though, and the team was looking for ways to activate even more tumor-killing cells. They decided to try tetanus, which is a vaccine that most Americans have received, safely, and one that activates a strong immune response.

“It's the same tetanus booster you get when you step on a rusty nail and have to go into the ER and get a shot,” said Kristen Batich of Duke University, who helped lead the study published in the journal Nature.

“So we enrolled 12 patients that we treated who underwent their standard care chemotherapy and radiation, which was done after their surgery, and then from there on they received our immunotherapy vaccine,” she told NBC News.

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The effects were remarkable. Patients who got the tetanus booster lived more than two years on average — about 26 months.

And one patient has lived eight years. She’s Sandy Hillburn, a 68-year-old grandmother living in Fort Lee, New Jersey.

When she was diagnosed in 2006, she was given two to three months to live. But her family had heard about work being done at Duke, and she flew there to join the study. First of all, she got surgery.

“They got all of the tumor that they could see,” Hillburn told NBC News.

But as with virtually all cancers that have spread, there were tiny tumor cells elsewhere in her body. That’s what the immunotherapy is designed to stop. Immune cells circulate throughout the body, patrolling for invaders such as bacteria and viruses, but also for mutant tumor cells.

Hillburn got a single tetanus shot, and then regular injections of the tumor-specific immune cells.

“What we think is going on is that tetanus this tetanus booster vacicine does such a good job at putting the immune system at high alert … it sort of puts the lymph nodes as well as the entire immune system on high alert, acting like a siren to the rest of the cells,” Batich said.

“And so the immune system knows to look for the next incoming danger signal. In this scenario it would be our immunotherapy vaccine that’s specific for the brain tumors in these patients.”

It’s not clear why the approach worked so well for Hillburn, who now enjoys playing with her grandsons.

“I’m so lucky,” she said. “I’m leading a very normal life, walk miles every day, play golf, I’m a retired bum, go to lunches with friends, I do class.”

She also travels to Duke for regular injections of the immune therapy that doctors believe is keeping the cancer at bay.

"It sort of puts the lymph nodes as well as the entire immune system on high alert, acting like a siren to the rest of the cells."

Nearly 23,000 Americans will be diagnosed with a brain tumor this year, and about 15 percent of these are the type called glioblastoma. Only about 30 percent of patients live for two years or more after diagnosis.

Even the patients who died enjoyed many months without symptoms, Batich said. “One of those patients was in the gym, lifting weights every day until a month before passing after the tumor grew out,” she said.

A larger study will start this summer, the researchers said.

Sandy, her case is not what we usually see in a patient with this type of tumor,” Batich said. “We are quite surprised, but given that her quality of life is very good, and that she recently received her 100th vaccine, we are very excited. But because this is something we don’t typically see, we don’t really know what to expect.”