At a major cancer research conference in the United States, scientists have shared the latest on an experimental vaccine for an extremely deadly cancer.

Pancreatic cancer is sometimes said to be the deadliest major cancer, because although it is relatively rare, roughly 87 percent of those diagnosed with the disease won't survive the next five years.

Even after decades of research, those outcomes have barely budged.

At last, new treatment options are in the pipeline, and one of the most promising therapeutic candidates is a personalized mRNA vaccine.

The medicine is still in clinical trials, but as of this year, researchers say seven patients with pancreatic cancer whose immune systems mounted a response to the vaccine they received are alive and well.

One of these patients was diagnosed with the deadly cancer at age 66 and received nine doses of the vaccine. She is now 72 years old, and she and her husband have celebrated their 50th wedding anniversary.

"There's no limitations on what I can do," the patient reports, "so for me it's absolutely been a miracle."

This particular vaccine for pancreatic cancer differs from other potential options, as it is made personally for each patient, using genetic material straight from their tumors after surgical removal.

The vaccine is thought to work by teaching the body's immune system to recognize and remember a specific type of cancer. These educated cells can then live for years, maybe even decades, potentially keeping the body safe from returning disease.

"We think we've found a way to awaken the immune system to prevent cancer from coming back," Robert Vonderheide, President-elect of the American Association for Cancer Research (AACR), told reporters at CBS8 news in San Diego.

"If we can do that, we can apply it to more patients with pancreas cancer, and, in fact, the strategy could have applicability to other types of cancer. We're really hopeful."

The latest findings from the phase 1 clinical trial were reported at this year's AACR annual meeting by oncologist Vinod Balachandran of the Memorial Sloan Kettering Cancer Center in the US.

"Now, at a 6-year follow-up, approximately 90 percent of these patients who generated [an immune] response remain alive," said Balachandran at the conference.

"So we think this is quite exciting for the field."

The phase 1 clinical trial included 16 patients with operable pancreatic cancer, whose disease had not yet spread to other parts of the body.

This cohort received the new personalized vaccine for pancreatic cancer following surgery, and they were also treated with immunotherapy drugs and chemotherapy.

After receiving the vaccine, eight patients showed positive immune responses, suggesting their T cells were primed to target cancer cells. Seven of these 'vaccine responders' were still alive up to six years after surgery.

Only two of the eight 'nonresponders' survived.

One of the surviving vaccine responders says he is now so healthy that he sometimes forgets all that he went through.

"I don't do a lot differently other than count my blessings every day because I'm a really lucky guy," he says.

Still, finding an operable form of pancreatic cancer is quite rare. This disease is insidious and is sometimes nicknamed the 'silent killer'. Some 90 percent of patients are diagnosed too late for surgery, which is one of the only routes to a cure.

In the most advanced stages, the five-year survival rate drops to 3.2 percent.

At this point, it is unknown whether an mRNA vaccine could extend life for those with more advanced stages of the disease, when the cancer has proliferated and spread.

"You have to take this with a little perspective, this is not treating hundreds of thousands of people," Brian Wolpin, director of the Gastrointestinal Cancer Center at the Dana-Farber Cancer Institute in the US, told NBC.

"The fact that they were able to use a vaccine to generate a response to new mutations that come up in the tumors, and then were able to show that this subsists, is promising."

In the US, pancreatic cancer is the third leading cause of cancer-related death, after lung and colon cancer. By 2030, it is predicted to take second place.

Very few treatments over the years have improved the cancer's survival rate.

mRNA vaccines have long been touted as a promising way to tackle cancer, even before the COVID-19 pandemic launched the technology into the limelight.

While the medicine shows great promise for skin cancers and other tumors, pancreatic cancer is a tricky one because it has fewer immune 'targets'.

This new research, however, suggests mRNA vaccines really can work for this type of cancer, at least in select cases.

"As we continue to learn more about how these vaccines work, there is a real belief and determination in the pancreatic cancer community that we can effectively treat this disease by training the patient's own immune system," says Balachandran.

"But continued progress requires continued research and testing."

A global phase 2 clinical trial is now underway.

The findings were presented at the annual meeting of the American Association for Cancer Research.