On the one hand, it is an expensive procedure. On the other, it benefits the medical community.

From Colonoscopies Finally Have an RCT by Zvi Mowshowitz.  The subheading is It did not match expectations.

Colonoscopies are an invasive screening test intended to prevent the emergence of colon cancer by early identification and treatment, and ultimately thereby reduce deaths from colon cancer.  While an outpatient treatment, it takes the better part of a day and costs a few thousand dollars.  Routine screening is usually recommended every three to five years after the age of fifty or so.  

It is a big medical industry amounting to some $35 billion a year.  When you add in lost productivity costs and ancillary cost, the price societal price tag would be higher still.

Much to many people's surprise, there has apparently never been a large RCT trial in terms of effectiveness.  We were doing them because it made logical sense to do them, not because we knew that they reduced either detected cancers or reduced deaths from cancer.  

In the past month the results of a first large scale rigorously designed RCT study of colonoscopy screening was released.  As Moshowitz notes, It did not match expectations.

This seems not dissimilar to cholesterol lowering drugs which have been prescribed since the early eighties to reduce the risk of heart attacks and the risk of death from heart attacks.  The first two big studies found that those being treated with cholesterol medications did have a lower death from heart attack incident rate.  But their overall, all-causes mortality rate remained the same.  

The evidence suggested that cholesterol medication reduced your chance of dying from a heart attack but raised the chances of your dying from other conditions and with no change in your overall all-cause mortality rate.

Cholesterol lowering medications is also about a $40 billion market.  

Moving on from the fact that two major branches of public health seem to involve a lot of cost and no benefit, we still have to address whether the most recent colonoscopy study is reliable.  

When I read the study, it appeared reasonably well designed and with a large population sample sizes.

On the other hand, I saw several fairly assertive counter-arguments which seemed to me to be tendentious but possibly viable given that they were speaking at a level of health detail beyond my kin.  I know enough to be skeptical but not enough to mount a viable refutation of their criticisms.

Fortunately, Mowshowitz, who does know this field (medical research) intimately apparently had the same reaction to some of the criticism and even more fortunately lays out his reasons in this essay.  Well worth a read.