There are more questions than answers regarding the most effective method to screen for colorectal cancer (CRC). Both colonoscopy and stool testing are viable screening strategies in certain populations and both have well-documented limitations. Head-to-head comparisons of the two techniques are currently under way, but final results are several years away.
“We are in a gray zone,” said Douglas J. Robertson, MD, MPH, co-principal investigator of a randomized controlled trial comparing the two testing modalities in 50,000 veterans. “We are still looking at intermediate results as we try to determine which method is better.”
Dr. Robertson will co-chair an AGA debate on Tuesday titled Colonoscopy vs. Stool Testing for Colon Cancer Screening. He is associate professor of medicine at The Dartmouth Institute for Health Policy & Clinical Practice and chief of gastroenterology at the White River Junction VA Medical Center in White River Junction, VT.
While colonoscopy is widely accepted as the gold standard for CRC screening in the U.S. based on observational studies, it has never been subject to randomized controlled trials (RCT) to establish absolute efficacy or effectiveness. Stool testing has both observational evidence and RCT support.
“When a patient asks which test is best, we don’t know the answer,” agreed session co-chair Aasma Shaukat, MD, MPH, a gastroenterologist and clinical researcher at the Minneapolis VA Health Care System, MN. “That makes screening, which is otherwise quite a simple concept, a more complex decision between patient, provider, resources and the health-care delivery system.”
There are multiple observational studies on colonoscopy screening, and multiple RCTs on stool testing. Observational data shows that colonoscopy is highly effective in detecting colorectal polyps and colorectal cancers. And the 10-year follow-up interval for a negative colonoscopy makes it attractive to patients.
At the same time, the intensive preparation needed for a high-quality colonoscopy makes the procedure unattractive to some patients. The procedure is expensive relative to stool testing, and the U.S. health-care system lacks the resources to screen all individuals over the age of 50 who are due for screening.
Stool testing is less bothersome for patients and is effective in reducing the incidence and the mortality of CRC. At the same time, stool testing has low sensitivity for precancerous polyps. It also requires annual testing, which can hinder compliance over time. But long-term follow-up studies suggest a protective effect lasting 30 years after screening, Dr. Shaukat said.
“At this time there’s clinical equipoise on what test is best, and every health-care delivery system must decide which test is best for getting the mass of the population screened, which is truly the purpose of screening,” Dr. Shaukat said.
At the patient level, there’s no simple answer for those who want to know which option is best. What clinicians can and should do is discuss the pros and cons of both methods, Dr. Robertson said. That discussion will become even more complex as new stool-testing methods are developed and introduced. In addition to the familiar fecal occult blood test, a DNA-based test for CRC has recently been approved for use in the U.S. and elsewhere.
Ultimately, compliance may be a key distinguishing factor.
“Studies that look at compliance with screening are crucial,” Dr. Robertson said. “People often focus simply on the sensitivity and specificity of a given screening test for detecting neoplasia. However, the real question is how compliant was your patient in getting tested? The test that gets done will likely be the most effective test for colorectal cancer screening.”
Please refer to the schedule-at-a-glance in today’s issue for the time and location of this and other DDW® events.