Is It the End of the Diagnostic Colonoscopy?
September 09, 2014

Is It the End of the Diagnostic Colonoscopy?

On August 11, 2014 the FDA approved Cologuard, a new screening test for colorectal cancer. A product of Exact Sciences in cooperation with the Mayo Clinic, the test is a noninvasive way to screen for colon cancer.

Here’s how it works.

You head to your doctor who has been hounding you for years to get a colonoscopy. All you really want is a refill of your Viagra, but you’re prepared for the inevitable lecture. But this time, he tells you to keep an eye out for the UPS man. The man in brown (so appropriate) will be dropping off a package with the Cologuard collection system at your house.

You will deposit a stool sample during your daily course of business and UPS sends it back to the Cologuard lab. There, the lab tests your sample for red blood cells and DNA indicative of cancer. They send a report to your doctor, who calls you to let you know that your test results are fine. But he was looking through your chart, and it's time for that prostate exam.

I wrote a little about a new colon cancer screening method called the PillCam a few weeks ago. These developments are a good thing, because colonoscopy carries significant risk, such as bowel perforation.

You’ll hear folks yelling that colonoscopy is the gold standard and these new screening options don’t come close to its accuracy.

That’s crazy talk and here’s why.

Cologuard has a sensitivity of 92 percent. That means it catches 92 percent of colorectal cancers but misses eight percent. Colonoscopy has a 95 percent sensitivity.

Of the approximately 141,000 new cases of colon cancer diagnosed each year, we would miss about 4,450 of them if everyone switched from colonoscopy to Cologuard. They won’t, but we’ll assume they will. We’ll also assume that all colorectal cancer diagnoses come from colonoscopy. They don’t.

Assuming all this, to make up for the 4,450 missed cancers, we would need to screen about 600,000 more individuals each year.

There are 20 million peoplein the U.S. who should be screened for colorectal cancer but aren’t.  So do the math: If one million can be convinced to collect a sample in the privacy of their own homes you’ll make up for all the missed cancers. If any of the other 19 million people go for it, not so many of us will die from colon cancer.

Why do I think lots of people will opt for the new test?

  • No risk of bowel perforation
  • No need for sedation
  • No need to find an available gastroenterologist and schedule an appointment
  • No need to miss work
  • No need for a driver to and from the appointment

What the test lacks in sensitivity, it makes up for in convenience and ease.

But, there is a problem that I foresee, and it’s something we need to be thinking about now –as individuals and as a society.

The current recommendation is to stop screening for colorectal cancer at age 75. Medicare, however, is going to approve payment for Cologuard up to age 85. So now we have a new issue. Although the risk associated with the screening test is all but gone, the risk of diagnosis remains the same.

A positive screening test requires a follow up colonoscopy and its risks to confirm the diagnosis. A diagnosis of cancer is followed by aggressive intervention, including surgery, radiation and chemotherapy.

Will the relative ease of screening with these new tests tempt us to screen at older and older ages? At ages where the risk of the diagnostic test - think bowel perforation again - itself is heightened?

Screening implies a willingness to treat. At what point will we be causing more harm than good in our elderly population?

As with every new technology, it’s important to think through long term implications. And as with every screening test, it’s probably best not to ask the question if you don’t really want to know the answer.

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