Longer Colonoscopies Linked to Lower Rate of Colorectal Cancer
Research by a Veterans Affairs team has confirmed that longer-lasting colonoscopies are associated with lower cancer rates. Their findings were published by Shaukat et al in Gastroenterology, and were based on nearly 77,000 screening colonoscopies.
Experts already know about the link between colonoscopy withdrawal time and patient outcomes, but the new study provides some of the strongest evidence yet to back clinical guidelines covering this aspect of the procedure.
“Our results support the use of withdrawal time as a quality indicator, as recommended by current guidelines,” said Aasma Shaukat, MD, MPH, with the Minneapolis VA Health Care System and the University of Minnesota.
Adhering to Guidelines
According to current guidelines, a “normal” colonoscopy—one in which there is no finding of cancer or precancerous growths, and the doctor does not remove any snippets of tissue to be biopsied—should have a withdrawal time of at least 6 minutes.
Dr. Shaukat's team looked at data on colonoscopies performed over 6 years by 51 gastroenterologists in a large community practice in Minnesota. The team calculated average withdrawal times for each doctor. The average for the practice on the whole was 8.6 minutes—well within guidelines. But about 10% of the doctors had individual averages of fewer than 6 minutes.
The researchers then checked the state's cancer registry to look for cases of colorectal cancer among patients who had been screened at the same practice during the study period.
Consequences of Shorter Withdrawal Times
Patients who had been examined by doctors with shorter withdrawal times, on average, were more likely to have cancer. The rate was more than twice as high for patients whose doctors had average withdrawal times of less than 6 minutes when compared with those whose physicians' average times were over 6 minutes.
Withdrawal times of longer than 8 minutes didn't seem to afford any extra reduction of risk. As such, the researchers say focusing quality-improvement efforts on withdrawal times of under 6 minutes would likely have the most impact.
The study included cancers that occurred within about 5 years of the patient's last colonoscopy. The assumption is that such “interval cancers” might have grown from polyps that were present during the colonoscopy but were not detected or fully removed.
Dr. Shaukat said the reasons for substandard withdrawal times may vary, but “generally, every physician aims to do a complete inspection of the colon lining, regardless of their withdrawal time.” Even the American College of Gastroenterology acknowledges that not every colonoscopy withdrawal must take at least 6 minutes, as some colons can be examined effectively in less than 6 minutes.
Just the same, Dr. Shaukat said that withdrawal time appears to be a “robust indicator” of interval cancer risk. She urges more research on the topic, and on related quality measures for colonoscopies.
“We need to understand the quality indicators better, define thresholds, and be able to adjust them to the particular patient population and underlying risk. Until there are uniform methods for data collection, adjustment, and collection, the numbers don't mean much.”
Dr. Shaukat said it is appropriate for patients to ask their gastroenterologists if they collect and review quality metrics for their colonoscopies. At the same time, though, she points out that most patients won't be in a position to properly make sense of the actual data.
“The exact metrics and their cutoffs are debatable, but a commitment to quality needs to be there for every practice.”
Dr. Shaukat is the corresponding author for the Gastroenterology article.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
