Is the best colorectal cancer screening test the one that gets done?

- Kenny Lin, MD, MPH

In 2008, the U.S. Preventive Services Task Force recommended routinely screening adults aged 50 to 75 years for colorectal cancer using fecal immunochemical testing (FIT), flexible sigmoidoscopy, or colonoscopy. At that time, it did not endorse two newer strategies, computed tomographic (CT) colonography and fecal DNA testing. But data from the National Health Interview Survey indicated that in 2013, only 60 percent of non-Hispanic white adults in the target age group was up-to-date on one of the three recommended colorectal cancer screening tests, with lower percentages for ethnic and racial minorities. Proponents of CT colonography and fecal DNA testing argued that more widespread insurance coverage of these "noninvasive" tests could potentially increase screening rates.

Earlier this month, JAMA published a USPSTF-commissioned systematic review of more recent studies and an analytic modeling study that compared the effects of different screening tests and strategies. The Task Force's updated recommendation statement said to screen adults aged 50 to 75 years, but expressed no clear preference about the "best" test or tests. A Figure that accompanied the statement showed that assuming perfect adherence, each screening strategy produces a similar number of life-years gained, with a colonoscopy-first strategy predictably leading to more total colonoscopies and procedure-related harms. Rather than recommending that eligible patients undergo a specific test, the USPSTF advised:

Given the lack of evidence from head-to-head comparative trials that any of the screening strategies have a greater net benefit than the others, clinicians should consider engaging patients in informed decision making about the screening strategy that would most likely result in completion, with high adherence over time, taking into consideration both the patient’s preferences and local availability.

Shared decision making is all well and good, but I am concerned about the communication challenges of expanding my standard discussion of colorectal cancer screening options from FIT versus colonoscopy (since physicians in my area no longer perform flexible sigmoidoscopy for colorectal cancer screening) to choosing between FIT, fecal DNA, CT colonography, and colonoscopy. I wish that the Task Force had provided more practical guidance about how primary care physicians can help individual patients select the "best" test for them.

Surprisingly for a group that typically has required the highest degree of evidence to justify an "A" rating, the USPSTF did not emphasize stool guaiac testing and flexible sigmoidoscopy, the only screening strategies that have reduced colorectal cancer deaths in randomized controlled trials. Earlier this year, the Canadian Task Force on Preventive Health Care did not recommend screening colonoscopy because it had not met that standard. (As Dr. Rita Redberg wrote in an editorial published simultaneously in JAMA Internal Medicine, "It would be interesting to know how many patients would undergo colonoscopy if they knew that there were no data to suggest that this procedure results in longer life.")

Finally, although the USPSTF reiterated that it "does not recommend routine screening for colorectal cancer in adults age 86 years and older," it omitted its previous "D" (don't do) recommendation against this unnecessary and potentially harmful practice. I think that this was a mistake. Plenty of octo- and nonagenarians still receive colorectal cancer screening tests; in a 2015 editorial, AFP editor Jay Siwek related his 90 year-old father-in-law's complications from a "routine" colonoscopy as an example of the harms caused by overscreening. The best test isn't only the one that gets done, but gets done in a patient who has a chance of benefiting from that test.