TUESDAY, Dec. 7, 2010 (HealthDay News) -- Stool tests that can detect blood from colorectal tumors are more accurate for patients on a low-dose aspirin regimen, which is known to increase intestinal bleeding, a new study suggests.
While therapeutic aspirin use was once feared to skew the results of fecal occult blood tests, or FOBTs, German researchers found the test was significantly more sensitive for low-dose aspirin users than for non-users. Future studies confirming the results could lead to recommendations to take small doses of aspirin before all such tests, gastroenterology experts said.
Aspirin's blood-thinning properties prompt some doctors to prescribe low-dose regimens (usually 75 mg or 80 mg) to those at risk of cardiovascular events such as heart attacks.
"We had expected that sensitivity was higher -- that is, that more tumors were detected," said lead researcher Dr. Hermann Brenner, a cancer statistics expert at the German Cancer Research Center in Heidelberg, Germany. "The surprising result was how strongly sensitivity was raised."
The study, conducted from 2005 to 2009, included 1,979 patients with an average age of 62; 233 were regular low-dose aspirin users, and 1,746 never used it. Researchers analyzed the sensitivity and accuracy of two fecal occult blood tests in detecting advanced colorectal neoplasms, tumors that can either be malignant or benign.
Participants were given stool collection instructions and devices, including bowel preparation for a later colonoscopy to verify results of the FOBTs. They self-reported aspirin and other medication use in standardized questionnaires.
Advanced tumors were found in the same percentage of aspirin users and non-users, but the sensitivity of both stool tests was significantly higher among those taking low-dose aspirin -- 70.8 percent versus 35.9 percent sensitivity on one test and 58.3 percent versus 32 percent on the second.
"The principle of stool tests in early detection of large bowel cancer is the detection of usually very small amounts of blood from the tumors," Brenner said. "Use of low-dose aspirin facilitates this detection."
His study is reported in the Dec. 8 issue of the Journal of the American Medical Association.
According to the American Cancer Society, colorectal cancer will kill about 51,300 Americans this year. It is the third most common type of malignancy found in men and women, with the exception of skin cancer.
"In the past, [giving aspirin] was felt you'd increase the bleeding from the stomach and be misled and think it was from the colon," said Dr. Felice Schnoll-Sussman, a gastroenterologist at New York-Presbyterian Hospital/Weill Cornell Medical Center in New York City.
"When the results are validated by colonoscopy, in that type of very pure setting, you're looking at this very sensitive test and proving (the aspirin) is not affecting specificity," Schnoll-Sussman said. "So we know that low-dose aspirin doesn't tamper with result and can enhance, for a very short time, the sensitivity of the test."
Dr. Frank A. Sinicrope, a professor of medicine and oncology at the Mayo Clinic, said while the study is "interesting and provocative," it is not definitive because it wasn't randomized. The pathology results also weren't independently reviewed, he noted.
However, Sinicrope and Schnoll-Sussman said it's possible that future guidelines for those taking stool screening tests -- usually individuals over age 50 -- will encourage low-dose aspirin use beforehand.
"Its a premature conclusion, but one suggested by these data," Sinicrope said, adding that a randomized trial would first be necessary.
"It will be important to replicate these findings in an even larger study," Brenner agreed.
More information
For more on colon cancer, visit the U.S. National Cancer Institute.
