DDW 2009: Fecal DNA Test a Quick, Noninvasive Check for Colorectal Cancer

Detection of "long DNA" in the stool, when combined with fecal occult blood testing, detects colorectal cancers with a specificity of 90%.

This approach is "among the best we have" for noninvasive testing of colorectal cancers, experts announced here at Digestive Disease Week 2009.

The test checks for nonapoptotic human DNA (long DNA) in the stool, lead investigator David A. Ahlquist, MD, from the Mayo Clinic in Rochester, Minnesota, explained during his presentation.

"Fecal long DNA may originate from either the exfoliation of dysplastic cells or from the luminal hemorrhage or exudation of leukocytes," Dr. Ahlquist said. "If leukocytes are the major source [of long DNA], then fecal human DNA and occult blood levels should correlate. If exfoliation is the major source, then fecal human DNA and occult blood should be complementary markers for colorectal cancer."

In a group of 70 patients with colorectal cancer, 27 with adenomas greater than 1 cm in diameter, and 70 healthy controls with normal colonoscopy, Dr. Ahlquist and colleagues sought to quantify and correlate human long DNA and occult blood in stool samples using polymerase chain reaction and the HemoQuant assay.

At 90% specificity, "long DNA testing detected 70% of colorectal cancers and 46% of adenomas, while occult blood testing detected 50% and 12%, respectively," Dr. Ahlquist reported.

"Combining these tests detected 80% of colorectal cancers and 46% of adenomas at 90% specificity."

The long DNA test was negative for healthy controls.

The area-under-the-curve values for detection of colorectal cancer were 0.82 for fecal long DNA, 0.78 for occult blood testing, and 0.90 for combination testing (P <>

In addition, "stool DNA testing detected cancers at each organ site, including 65% of esophageal cancers, 62% of pancreatic cancers, and 75% of bile duct and gallbladder cancers," said Dr. Ahlquist.

"In this series, 100% of both stomach and colorectal cancers were detected. . . . Importantly, stool test results did not differ by cancer stage," he told Medscape Gastroenterology. "Early-stage cancers were just as likely to be detected as late-stage cancers."

"This is a continuing story. . . . It's like the Holy Grail," Lawrence Brandt, MD, from Montefiore Medical Center and professor of medicine at the Albert Einstein College of Medicine in the Bronx, New York, said in an interview after Dr. Ahlquist's presentation. "We keep looking for a better way to noninvasively test for colorectal cancers."

If this is confirmed in larger studies, this will be among the best [noninvasive] test that we will have."

"Dr. Ahlquist has been doing this a long time," Dr. Brandt said. "I look forward to seeing what he does."

"We anticipate that next-generation tests will also be able to predict the tumor site, which will help physicians direct diagnostic studies and minimize unnecessary procedures," Dr. Ahlquist said.