New DNA test may improve cancer screening

The digestive tract
The human digestive tract. Cancers that occur in many locations in the digestive tract are difficult to detect in early stages. Doctors at the Mayo Clinic are researching a new DNA test which could lead to earlier screening for cancer in these parts of the body.
Image courtesy of LadyofHats via WikiMedia Commons

Gastrointestinal cancers -- those found in the esophagus, pancreas, stomach and other organs -- are difficult to diagnose.

"None of the cancers above the colon are currently screened," said David Ahlquist, a gastroenterologist at Mayo. "And yet they account for more than twice the number of deaths compared to colon cancer." For example, only five percent of people diagnosed with pancreatic cancer survive because it usually isn't found until the late stages of the disease. Ahlquist says early detection would increase the survival rate.

Ahlquist has previously studied the use of stool DNA tests in colon cancer. In this research, he screened samples for signs of cancer higher up in the digestive system as well as in the colon.

Dr. David Ahlquist
Dr. David Ahlquist of the Mayo Clinic say a new DNA screening may be able to identify some hard-to-detect gastrointestinal cancers.
Photo courtesy of the Mayo Clinic

Cancer cells have mutated DNA, which researchers look for in the analysis. The testing is sophisticated enough that it can determine where the cancer is in the body.

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"What's common to all of these cancers is that they shed cells into the GI passageway that are ultimately excreted with stool," Ahlquist said. "So by doing a stool DNA test, one has the potential to detect all of these cancers."

Ahlquist's researchers analyzed 140 samples, 70 from people with known GI cancers, and 70 from people without cancer. Of those, 100 percent of the stomach and colon cancers were detected. But only 62 percent of pancreatic cancers were detected. Early-stage cancers were as likely to be found as late stage.

Dr. Selwyn Vickers, Associate Director of the Masonic Cancer Center at the University of Minnesota, says these findings are hopeful for pancreatic cancer, which has no screening available currently.

"So this is a flicker of light in the room for pancreas cancer," he said. "But there is still a long way to go before we can say its application is going to bring value. It does bring hope, and those are two different things." He says the accuracy rates right now, at 70 percent, are too low.

"Screening test says you don't have a cancer. We checked your stool. Go on and live your life. Mr. Jones comes back six months later and he now can't move his bowels because he now has a cancer. And he comes back to say to you, Doctor, you did that test, didn't you say I didn't have cancer? And you say, yeah, but it's not 100 percent, in fact it's really not more than 70 percent."

Tests like these have a checkered history, not just in colon cancer but also in ovarian and prostate cancers. But Dr. Durado Brooks of the American Cancer Society says recent stool screening tests have been useful in colorectal cancers.

"If that same level of accuracy, or even greater levels of accuracy, can be found for other gastrointestinal cancers then this test would have utility. But we're simply too early in the process to know whether that's the case or not. It's going to take a lot more work looking at populations who are presumed to be well."

An abstract of these findings was published in Gastroenterology. The research is being presented Tuesday at a conference in Chicago.