July 19, 2018
A New Screening Test for Colon Cancer

A New Screening Test for Colon Cancer

by Berkeley Wellness  

Several readers of the University of California, Berkeley Wellness Letter have asked about the relatively new screening test for colorectal cancer called Cologuard, wanting to know if it’s a good—or even the “best”—option, especially if they want to avoid a colonoscopy.

Cologuard is a stool test that screens for colorectal cancer and advanced adenomas (polyps at higher risk for becoming cancer) two ways: by checking for DNA markers and by looking for hemoglobin from blood in the stool via a fecal immunochemical test (FIT). Available by prescription, it was approved by the FDA in 2014 for screening people over 50 at average risk for colorectal cancer. As with other stool tests, you use a kit at home to collect a stool sample and mail it to a lab for analysis. If you get a positive result, you’ll need to have a colonoscopy to confirm (or refute) the findings and remove any polyps or cancer that may be present. The FDA and Medicare have cleared the test to be repeated every three years, though there’s no published research showing that this is the optimal screening interval.

It’s good to have this as another screen­ing option, since one-third of Americans have not been screened as recommended. Some of them may be attracted by Colo­guard’s genetic underpinnings and direct-to-consumer advertising. But it’s not known how Cologuard (that is, FIT-DNA test) compares to the other colorectal cancer screening tests in terms of saving lives and minimizing overdiagnosis and overtreatment, since it is new and there has been less research on it. The other rec­ommended screening tests are colonoscopy (usually every 10 years), annual stool tests for blood (notably FIT, which is most accurate), and sigmoidoscopy (usually every five years, along with stool tests every three years).

Unanswered questions about Cologuard

The only published study on Cologuard screening for the general population was a large clinical trial in the New England Jour­nal of Medicine in 2014. It gave Cologuard a boost when it found that the test detected more cancers and advanced adenomas than one-time use of FIT. There were some caveats, however. Cologuard produced more than twice as many false positives as FIT; such false alarms lead to more unnecessary colonoscopies and needless anxiety. And for about 6 percent of people undertaking Colo­guard testing, the stool samples they sent in could not be analyzed (compared to just 0.3 percent of those using FIT). Most likely this was because the stool collection procedure for Cologuard is more complicated than for FIT and harder to do correctly.

Moreover, the study’s comparison between Cologuard and FIT was not really fair, since it’s recommended that FIT be done annually, not just once every three years like Cologuard. A longer-term study comparing Cologuard every three years to FIT screening repeated annually would have more real-world relevance.

Cologuard costs 20 to 30 times more than FIT—as much as $650. Medicare covers it, but many private insurers do not.

In its updated draft guidelines for colorectal cancer, released in October 2015, the influential U.S. Preventive Services Task Force said there is insufficient evidence to recommend Cologuard for routine screening, citing "greater uncertainty" about its "net benefits." However, the final guidelines, published in June 2016, include it among the screening options, with the caveats that it may result in "more false-positive results, more diagnostic colonoscopies, and more associated adverse events per screening test" and that "at present, evidence is lacking to establish the optimal frequency of screening with the FIT-DNA test."

There still is no “best” screening test for colorectal cancer. The key is just to get screened, period. For more about your options, go to Colon Cancer Screening Choices.

Originally published November 2015. Updated July 2016.