CATEGORY: GUT & DIGESTIVE HEALTH
If you’ve been putting off a colonoscopy, the alternative usually arrives as a small kit in the mail. Among 20,176 U.S. adults who tried both kinds of kit before a screening colonoscopy, a next-generation stool DNA test—marketed under the brand name Cologuard Plus—caught 93.9% of the colorectal cancers the colonoscopy went on to find, while the standard fecal immunochemical test (FIT), a category of at-home kit sold under several brand names that checks for hidden blood in the stool, caught 67.3%.1 The newer test also raised more false alarms. Both halves of that result matter.
Everyone Took Both Tests, Then the Colonoscopy Settled It
Nobody was assigned to one test or the other. Every participant took both. Adults 40 and older who were already due for routine screening at 186 U.S. centers sent in a stool sample, which was run through the DNA test and through the blood-detecting kit. The DNA test looks for altered DNA that tumors and polyps shed into the stool, along with traces of blood. Then each participant had a colonoscopy, and that exam served as the answer key. It turned up 98 cancers and 2,144 advanced precancerous growths, the polyps most likely to turn into cancer over time. Because everyone got the full exam, the researchers could score each kit against what was really there. One disclosure matters: the study was funded by Exact Sciences, the company that makes the DNA test sold as Cologuard Plus.1
What It Caught, and What It Flagged by Mistake
The DNA test noticed 93.9% of the cancers, against 67.3% for the standard kit. It found 43.4% of the advanced precancerous growths, against 23.3%. That second pair of numbers cuts both ways. It’s nearly double the standard kit’s rate, and it still means more than half of the most worrisome polyps slipped past unseen. The extra sensitivity had a cost among people whose colons were fine. Out of every 100 of them, the DNA test wrongly flagged about nine; the standard kit flagged about five. A flag was not a diagnosis. Bleeding from harmless causes, and DNA changes shed by ordinary polyps, can trip these tests, which is why every flagged result in the study was checked against the colonoscopy. The researchers write that this new version was developed above all to improve specificity, the false-alarm side of screening.1 It still raises more false alarms than the standard kit does.
The Blood Test in the Same Journal Issue Did Less
The same week, the same journal published results for a screening blood test, now marketed under the brand name Shield. It detected 83.1% of colorectal cancers but only 13.2% of advanced precancerous growths.2 Lined up together, the options form a pattern. Colonoscopy sees and removes polyps directly. Stool DNA testing catches some of them. Blood testing catches cancer reasonably well and precancer barely at all. None of these results says which strategy saves the most lives over decades of screening. That takes long outcome trials, and for the newer tests those don’t exist yet. What this head-to-head does show is how much more a single round of the new stool test notices, and how many extra false alarms come with it.
Key Takeaways
- The next-generation stool DNA test (Cologuard Plus) found 93.9% of colorectal cancers in one round of screening; the standard fecal immunochemical test (FIT) found 67.3%.
- False alarms were more common with the DNA test: about 9 in 100 people with clean colonoscopies were flagged, versus about 5 in 100 with the standard kit.
- More than half of advanced precancerous polyps still went undetected by the DNA test, so it’s far better at finding cancer than at finding what might become cancer.
- This was a one-round accuracy comparison scored against colonoscopy, not a trial of whether either kit prevents cancer deaths over years of use.
References
- Imperiale TF, Porter K, Zella J, et al. Next-Generation Multitarget Stool DNA Test for Colorectal Cancer Screening. New England Journal of Medicine. 2024;390(11):984–993. link
- Chung DC, Gray DM, Singh H, et al. A Cell-free DNA Blood-Based Test for Colorectal Cancer Screening. New England Journal of Medicine. 2024;390(11):973–983. link