Setting the record straight: New stool DNA test for Colorectal Cancer Screening (A guest Blog by @DrDeborahFisher)

 

A bit about today’s Blog Post…..

Dr Deborah Fisher is a brilliant Gastroenterologist at Duke University Medical Center.  She is also a fantastic wife and mother.  A Twitter fanatic, Dr Fisher has taken to Social Media to promote issues in Gastroenterology.  Today, she writes about a very controversial subject in GI–Does a New stool DNA test Replace Colonoscopy and is the Media Creating Confusion in the Market? 

Setting the record straight: New stool DNA test for Colorectal Cancer Screening (A guest Blog by @DrDeborahFisher) 

An occupational hazard of being married to a rising media star is that when I expressed my concern and exasperation at the misinformation being circulated about a newly FDA-approved colorectal cancer screening test, his response was “write a guest blog for my blog page”. Another occupational hazard is having the local NBC-affiliate news truck parked in front of our house at 9:30 on a random summer evening. But that is for another blog.

For full disclosure, I am a gastroenterologist and much of my research and clinical focus is colorectal cancer screening. Some of my previous comments on the new stool DNA test, Cologuard, have already been published in the New York Times as well as in a previous issue of @MedPageToday. However, I have recently noticed a number of misleading articles in various newspapers across the country and wanted to address these, likely common, misconceptions about the new test.

First, I want to openly acknowledge the positives about Cologuard. The study in the New England Journal of Medicine examining its ability to find a colon or rectal cancer as a one-time test (compared to colonoscopy as the gold standard) was large, well-designed and well-executed. It showed that as a one-time test Cologuard was 92% sensitive for cancer. It also showed that the false positive rate was about 13%.

The problem has arisen in how the study results are being spun in the media. Here are a couple emerging myths to debunk:

  • Cologuard is for patients who absolutely positively want to avoid colonoscopy.

                                                     FALSE

While colonoscopy is the most common test used in the US to screen for colorectal cancer , it is not the only test. It is not even the “best” test. It is the most accurate test for finding cancers and polyps but that is not the same as the “best” because there are clear downsides including cost, risk of complications, access. A screening strategy of using a non-invasive test first can greatly decrease the need for colonoscopy but does not eliminate colonoscopy because Positive Screening Tests Should Be Followed By a COLONOSCOPY. Therefore, a positive stool DNA test needs to be evaluated with colonoscopy or the point and potential value of screening is lost.

The fecal immunochemical test, aka FIT, is also a non-invasive colorectal cancer screening test. It has been around for decades, and in its current form is a widely available test that is included in all the US colorectal cancer screening guidelines

In fact, I will argue that it is a better test for your patient who is not completely against screening but would prefer to avoid colonoscopy if possible because 1) its false positive rate is 5% vs. 13% for Cologuard. Therefore it carries a lower risk of leading to an unnecessary colonoscopy 2) it is currently covered by all insurance carriers

  • Cologuard will increase colorectal cancer screening rates in the US population

                                                       FALSE

Or perhaps a more accurate response might be “We have no idea” since it is a new test and the only people who have used it were in a research study.

On the other hand, we have compelling data that FIT increases screening rates compared to the older guaiac-based fecal tests and among patients who were previously unscreened.

 

  • Cologuard is the best non-invasive test for colorectal cancer screening

                                                       FALSE

And a bit of a trick question because we really do not have a Best Test at this point. Nonetheless, Exact Science is clearly going after the screening market leftover after colonoscopy takes its lion’s share. In addition to my general case for no “best” test, I would argue that Cologuard has not accumulated enough data to knock FIT off its best non-invasive test perch.

Yes, Cologuard had a higher rate of diagnosing cancer in one-time testing compared to a single FIT product in a single study, but

1) Screening is not a one-time test. FIT is meant to be repeated annually (or biennially in most screening programs outside the US). We have no idea if after 2 or 3 rounds of FIT the higher sensitivity (detecting cancer among individuals with cancer) of Cologuard will remain.

2) The interval of annual FIT testing has a wealth of data support vs. no data whatsoever supporting ANY testing interval for stool DNA tests (currently CMS is considering a 3 year interval

3) In a healthy population, it is important to consider harms and the higher rate of false positives leading to colonoscopy could translate into an increased rate of adverse events.

4) FIT is $25 vs. $600 for Cologuard

 

Now, some might say, “hey colonoscopy is the most expensive, risky option out there”. To which I say touché. Perhaps unfortunately, no headlines are claiming any test is better than colonoscopy. That might be another blog. Poor Dr Campbell is creating a social media monster.

Deborah Fisher, MD, MHS

Associate Professor of Medicine

Duke University Department of Medicine

Division of Gastroenterology

@DrDeborahFisher

Photo on 6-16-14 at 2.49 PM #3

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