In the clinical trial Cologuard detected 92% of colorectal cancers (8% false negative rate) and 42% of precancerous lesions. The trial involved over 10,000 patients scheduled for screening colonoscopy, which subsequently identified colorectal cancer in 65 patients and advanced precancerous lesions in 757. The test reportedly has an approximately 13% false positive rate of diagnosis. Doing the math, this means that the test detected 60 of the 65 cancers and 325 of the adenomas. However, it was found to detect almost 70% of the adenomas believed to be most likely to progress to cancer. With a 13% false positive rate, this means that about 1300 people were found to be positive for the test who were clear on colonoscopy.
How does this compare to fecal occult blood testing? Fecal immunological testing (FIT) was 73% sensitive detecting only 48 cancers. However, it had only a 5% false positive rate.
Of course there are questions and doubters. In the LA Times, they quoted the head of the endoscopy unit at UCLA:
Dr. Bennett Roth, a professor of gastroenterology at UCLA, took a more measured approach to Cologuard. He said the test is still a work in progress, "but it's a move in the right direction." Roth said, is that it could encourage more people to have a colonoscopy, which remains the gold standard for diagnosing and treating colon cancer. "Maybe if you get a positive test with Cologuard, you'd be convinced to have the more definitive test," he said. "It doesn't replace the need for a colonoscopy."I am not so sure I would interpret the results this way. Colonoscopy is not without its issues. There is reported incidence of serious adverse events of 2.8/1000 procedures. Eight people per 10,000 patients screened will have a perforation. Hemorrhage occurs in 1-6 per 1000 colonoscopies.
Furthermore, colonoscopy is far from perfect (reference). The cancer miss rate (false negative) is reported to be as high as 6% and the adenoma miss rate for tumors greater than 1 cm is 12-17%. Perhaps some of the false positives detected by DNA testing may not be false positives at all?
I have news for Dr. Roth. Perhaps your position heading an endoscopy group has clouded your thinking about value. I cannot help but think that if I were to go and ask a president of a life insurance company about the value of life insurance, I might get a similar skewed perspective. Of course everyone should have life insurance!
I have had my colonoscopy when I was around age 50 and soon enough someone will raise this with me again. Hmmm... let me think about this? There is a test available which is nearly as sensitive, with no prep, no anesthesia, no invasive risks, and it can be obtained at a fraction of the cost....Can you say no-brainer!
Let me do some additional math. This test roughly may eliminate the need to do over 80% of the $14 billion colonoscopy market. As Dr. Roth noted, perhaps this test may convince selected people to undergo colonoscopy, since 1/3 of the targeted screening group (50-75 year olds) are not screened. Even capturing this entire group, you would only expect perhaps 10% of these people to undergo colonoscopy.
I think any way you look at this this test represents a likely disruptive technology which will change the economics of GI medicine. Perhaps there are aesthetic medicine opportunities. Everyone else is doing it!