Colorectal Cancer: To Screen or Not?

Kenneth W. Lin, MD, MPH


December 05, 2019

Editorial Collaboration

Medscape &

This transcript has been edited for clarity.

Hi, everyone. I'm Dr Kenny Lin. I am a family physician at Georgetown University. Medical Center, and I blog at Common Sense Family Doctor.

A fellow Medscape commentator, Dr David Johnson, a gastroenterologist at Eastern Virginia Medical School, recently criticized a clinical practice guideline on colorectal cancer screening that appeared in the BMJ earlier this year. Developed by an international author team, this guideline diverged from American guidelines, including a recent guidance statement from the American College of Physicians, by recommending that the decision to screen be based on a patient's estimated 15-year risk of developing colorectal cancer rather than on a universal age range. The guideline authors proposed using a United Kingdom–developed tool called QCancer to estimate colorectal cancer risk, and only screening patients with a risk of 3% or greater.

In his commentary, Johnson raised several concerns. First, the QCancer tool does not include African Americans as a demographic category, which is problematic because they are at higher risk for colorectal cancer and more likely to die from it. Most Caucasian men and women will not reach the 3% risk threshold until sometime in their 60s, considerably later than the recommended starting ages of 45 or 50 from the American Cancer Society or the US Preventive Services Task Force (currently under revision), respectively. Finally, noting that colorectal cancer and mortality have declined in the past two decades, he suggested that screening fewer people at later ages has the potential to reverse this progress.

I would like to provide a primary care perspective. Although certainly important, colorectal cancer screening is one of several recommended preventive services I provide to older adults. It is appropriate to weigh the potential benefits of colorectal cancer screening against its burdens and potential harms. At a minimum, patients who undergo a colonoscopy for primary screening purposes or evaluation of a positive fecal test will require bowel prep and need to miss work or forgo some other planned activity. And the best estimates are that 1 in 1000 colonoscopies result in serious bleeding, 1 in 2000 result in bowel perforation, and 1 in 33,000 lead to death, with older patients more likely to experience these harms.

Individual endoscopists all claim that their complication rates are lower than these averages, but this Lake Wobegon effect can make doctors too eager to screen patients with a low likelihood of benefit. In my practice, I see as many examples of overuse of screening colonoscopy as I do underuse. In one study, 88% of repeat colonoscopies following a completely normal colonoscopy occurred after less than 9 years rather than 10 years, as recommended by guidelines. Another study found that in a sample of Medicare patients who received at least one screening colonoscopy, 25% had an estimated life expectancy of less than 10 years.

In a perfect world, every eligible adult would receive some form of colorectal cancer screening, surveillance colonoscopies would only occur at guideline-recommended intervals, and these tests would be associated with zero burden and complications. But in the real world, patients' preferences, values, and personalized likelihood of benefit or harm from a screening test should matter a great deal. Although I will continue to routinely offer colorectal cancer screening to patients between the ages of 50 and 75, I also intend to discuss the differing guidelines and their limitations, and allow patients to make better informed decisions.

This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.

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