Cologuard is a good screening tool. It's not as good as colonoscopy but does have obvious advantages, not the least of which is that many people who refuse colonoscopy screening for colon cancer will pay the $600 for Cologuard and get screened that way. As a result...many more people are getting screened, which is a good thing. It's also a good thing for doctors who do colonoscopy, since the more people screened, the more people get colonoscopy. This is because there are more people, and because of the false positive rate. The result is a substantial net gain in the number of colonoscopies being done. Add in the fact that colorectal cancer screening is now moving to begin at age 45 instead of 50...well, we're getting to the point where there just aren't enough colonoscopes or doctors qualified to use them. The colonoscopy business is booming.
When doctors do any kind of screening test, two concepts of primary concern are the false negative rate and the false positive rate. Obviously, it's better to have a false positive than a false negative. Fortunately for patients, Cologuard's false negative rate for colon cancer is low. Fortunately for colonoscopists, the false positive rate is high.
Regarding the false negative rate...it's low, about 0.1%, for cancer. But about a third (33%) of the patients with a "negative" Cologuard will have one or more pre-cancerous polyps many of which, if left in place will advance to a colon cancer, and might do so within the recommended three-year screening interval. IOW, only about 2/3 of people (66%) with a negative Cologuard have a truly negative Cologuard. The concern that this high number of missed colon polyps raises is the result of the long-awaited long-term studies on the rates of colonoscopy screening programs, with polyp removal, on the incidence of colon cancer. Those studies showed a clear reduction in the number of colon cancers found due to the fact that those screening colonoscopies found and removed colon polyps before they could become cancerous. One has to therefore wonder about the long-term results of the fact that a negative Cologuard may well mean that now a substantial number of patients will have pre-cancerous colon polyps left in place, at least until they get big enough (or cancerous enough) to shed more detectable DNA.
The overall false-positive rate for Cologuard is about 10%. It's worth noting that that rate rises noticeably in the older population (>age 60) due to changes in the stability of the shed DNA in older people.
Overall, Cologuard is a good screening tool for colon cancer and a fairly good test for pre-cancerous polyps in the colon. We'll have to wait for long-term tests (20 years or so) to find out how well it affects both colon cancer rates, and colon cancer survival.
ETA:
Couple of other thoughts...Cologuard shouldn't be used in people who might have occult bleeding into the colon but that's a tough call. It might include endurance athletes, but 68 year-old endurance athletes are a pretty small patient population, especially compared to the number of patients with hemorrhoids. Throw in the number of people who are taking vitamins with iron or who ate a hamburger or steak dinner within the previous 3-4 days. The downside, as noted, is that insurance will generally pay for screening colonoscopy, but if you've had a positive Cologuard, you will have to have a colonoscopy and now that is no longer a screening colonoscopy, so deductibles and co-pays apply. Surprise!
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Last edited by Cuyuna; 12-09-18 at 08:59 AM.