Blood test holds promise for earlier pancreatic cancer detection

Researchers say an experimental blood test shows promise for detecting pancreatic cancer earlier.

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Pancreatic cancer is an especially tough cancer to beat because it usually isn't detected until late in the disease. But a new blood test that uses two protein markers is showing promise for picking it up earlier, researchers report.

The blood test is still in the investigative stages. A new study, published in Science Translational Medicine, finds it works with an 87 percent sensitivity, meaning that's how often it can correctly identify someone with stage 1 or 2 pancreatic cancer. It also had 98 percent specificity, meaning the ability to accurately rule out cancer in a person who doesn't have it.

"What we found is a biomarker panel that's very cheaply, conveniently assayed in the blood and that uses conventional methods used by diagnostic centers around the country. So it could be used to detect pancreatic cancer at stages 1 and 2," study author Kenneth Zaret, director of the Penn Institute for Regenerative Medicine, told CBS News. 

The 5-year survival rate for pancreatic cancer patients is only 7 percent, and it's projected to become the second leading cause of cancer death in the United States by 2020.

Zaret worked with Gloria Petersen, from the Mayo Clinic, to identify a pair of biomarkers that physicians could soon use to discover the disease earlier.

Zaret began searching for a way to detect pancreatic cancer earlier after his own mother-in-law passed away from it about 15 years ago.

At the time, scientists were primarily studying late-stage cancer tissues in the lab in order to identify biomarkers for the disease in cells, in the hopes of developing a blood test for pancreatic cancer.

"But I didn't see how that could detect early stage markers," said Zaret, whose expertise is in genetics and stem cell biology, not cancer.

"I came from outside the field and applied genetic reprogramming methods so that's where the novelty is in terms of discovery," he said.

He and colleagues took late stage pancreatic cancer cells and reprogrammed them genetically to a "stem cell-like state" – what's called an induced pluripotent stem cell.

"Like an early embryonic stem cell," he said.

Then they let those cells redevelop into differentiated cell types and the cells underwent a progression from early to late stage cancer.

Using those cells, they discovered 107 proteins released from early stage pancreatic cancer cells. From there, they looked for those proteins, which could be found in very low levels in human blood and that would be easy to test for based on current blood lab technologies.

"From those we found a marker called THBS2," said Zaret.

Serum levels of THBS2 were significantly elevated in blood samples from 81 pancreatic cancer patients compared to 80 healthy people who served as the control group.

While the results were promising, "they were not powerful enough to do something statistically with," said Zaret. 

So the scientists further improved the test's sensitivity and specificity by combining it with another protein, CA19-9, already being used as a clinical marker. They analyzed samples from 197 cancer patients, 140 healthy people in a control group, and 200 people with pancreatic disorders that weren't linked to cancer.

The combination THBS2 and CA19-9 ratcheted up the test's accuracy to 98 percent. They believe it could serve as a low cost way to screen higher risk people — someone with a relative with the disease, or who has diabetes, for example — for pancreatic cancer.

"The bottom line is, by looking at two markers and not just the single marker we increased the range of what we could detect in a person with pancreatic cancer," said Zaret.

Combining his background with the expertise of colleagues at the Mayo Clinic made the discovery possible.

"We collaborated with Dr. Gloria Petersen at the Mayo Clinic in Minnesota. She is an expert in obtaining blood samples from pancreatic cancer patients and controlling for age, sex, and other parameters. So we had a very rigorous study. The extreme care with which we matched patients and controls is part of the strength of our work," he said.

The next step in their work is to use the test in more and more patients, specifically those at higher risk for pancreatic cancer.

"It will let us assess whether our biomarker test will allow us to detect cancer even before it is stage 1," said Zaret — "stage negative 1," so to speak.

"Our big goal is to be able to detect pancreatic cancer before it's at the 13 percent survival rate, which is where a stage 1 diagnosis is now."

If that succeeds, doctors would be able to identify more patients earlier, raising hopes of achieving higher survival rates for pancreatic cancer down the road.

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