Sunday, October 16, 2022

New Study Questions Screening Colonoscopy - Doctors Push Back

Colonoscopy became ‘breaking news’ about a week ago.  The preeminent medical journal, The New England Journal of Medicine (NEJM) published a randomized trial assessing the effectiveness of screening colonoscopy in reducing the risk of contracting colon cancer and dying from it.  The results were lackluster.

While there is accumulated evidence that colonoscopy can reduce colon cancer risk, the bulk of this data has not been the results of randomized controlled trials, the gold standard in medical research.  In the NEJM study, there was a group who was offered a screening colonoscopy and a separate control group who was not.

Gastroenterologists, along with the medical community at large, have been preaching the lifesaving benefits of screening colonoscopy for decades.  The simple strategy is to remove ‘pre-cancerous’ polyps that are lurking silently in the colon and to remove them before they have an opportunity to transform into cancer.  What makes colonoscopy such an attractive screening tool is that is can destroy a precursor to colon cancer – a benign polyp – which can remain dormant for years.  Other cancers, such as lung and pancreatic cancers, do not have ‘pre-cancerous’ lesions like colon polyps that can be easily screened for and removed.  This is one reason why these cancers often announce themselves after they have already spread. 

In the NEJM study, the group who was offered screening colonoscopy had an 18% reduction in developing colon cancer, a statistic much lower than prevailing opinion. Let me illustrate how modest an 18% reduction truly is. If your lifetime risk of developing colon cancer is 4%, then an 18% reduction lowers your risk to 3.28%.  In other words, you won’t enjoy much benefit with this risk reduction even though an 18% decrease may sound substantial.  In the NEJM study, it was calculated that for every 455 patients invited into the colonoscopy arm of the trial, 1 case of colon cancer would be prevented.  I’ll let readers decide if this statistic represents a game changer. 

Colon cancer under the microscope.
Is colonoscopy the weapon we thought it was?

As expected, professional gastroenterology societies argued that the study was flawed for several reasons and argued that screening colonoscopy does protect patients from colon cancer.  I felt that their criticisms of the study were legitimate.  However, I wondered if they would have voiced these same concerns if the study concluded that colonoscopy was highly effective.  

As one who has read many of these studies over the years, I don’t think we truly know to what extent colonoscopy reduces risk and mortality.  Shouldn’t we know this when designing colon cancer prevention strategies for the public?  Colon cancer screening is difficult to study as it may take a decade or longer to demonstrate a benefit when the rate of colon cancer development is very low and the disease is relatively uncommon.  It’s much easier for investigators to show that an intervention is effective when a disease is more common.

I have done more than 50,000 colonoscopies thus far in my career.  Have I saved lives?  I certainly hope so, but perhaps less so than I had thought.  The vast majority of my colonoscopies have been normal or have discovered small polyps, which I removed.   Gastroenterologists have no method to determine which polyp may be at risk of malignant transformation.  That is why scour the colon and remove any and all polyps encountered.  But, most of them will remain benign and innocent.  We are using a wide net.

How much risk reduction would justify screening every adult starting at age 45, which is the new recommended age to begin screening.?  I doubt 18% would be the holy grail.  Even doubling this to 36% risk reduction seems modest to me.  I’ll bet if you asked most doctors, including gastroenterologists, how effective colonoscopy is, you would likely hear much more optimistic responses than is justified by existing data, including this latest study.  Same issue with mammography.  The actual benefit that women enjoy from this test is much less than most of them, and perhaps their doctors, believe.

I still recommend screening colonoscopies to my patients, but we will have to see how all of this shakes out.  And the issue will be moot as new technologies such as stool or blood testing will soon render the colonoscope obsolete. 


  1. There is no way you have done over 50,000 colonoscopies. Assuming you have been doing these procedure for about 30 years, that would mean you have been averaging 1667 colonoscopies per year since day one of completing your fellowship. Assuming colonoscopies are predominantly done on weekdays (with perhaps a rather small number of urgent weekend colonoscopies), that would mean you are averaging over 33 colonoscopies each and every day. This an unreachable and absurdly high number. Unless you are 90, I believe you are greatly exaggerating

  2. @anonymous, Thanks for reaching out. While your point is somewhat peripheral to the central point of the post, I will respond. As I having been doing procedures for nearly 35 years, I respectfully suggest that your math may be slightly off. But, let’s not quarrel over this. I’m more interested to hear your view of my post’s view on the recent NEJM colonoscopy study.