Most folks don’t like going to the doctor’s office, and nearly everyone hates “needles”, whether they be fingersticks, blood tests, or getting your flu shot.

But if you would ask people what is the worst test they ever had, they would say either a Barium Enema or a Colonoscopy.

Yet cancer of the large bowel is a killer, and when someone has symptoms (blood in the BM or change of bowel habits) docs order one of these tests to try to make sure it’s not cancer.

Which test is done depends on where you live, but most of us nowadays rely on the colonoscopy if it is available (although the double contrast Barium Enema with a sigmoidoscopy is also a good test, and there is a newer CT scan being done that might work too).

The reason is technical: The Barium enema is fairly easy to do, but it doesn’t check the last 10 inches of the intestines well, so you have to check that with a signoidoscopy, which is sort of like a colonoscopy but the tube is a lot shorter. Most docs can do a sigmoidoscopy, whereas it takes a bit of training to do a decent colonoscopy.

But now the NYTimes says that colonoscopies are worth the money:
Colonoscopy lowers the rate of colon cancer by 50 percent.

A new study provides what independent researchers call the best evidence yet that colonoscopy — perhaps the most unloved cancer screening test — prevents deaths. Although many people have assumed that colonoscopy must save lives because it is so often recommended, strong evidence has been lacking until now.

Yes, now they have proof, so it means the gov’t may actually pay for these tests.

Wait: It should be lowering the rate 100 percent, since you are taking out the pre cancerous polyps, right?


The transition from benign adenoma to colorectal cancer is thought to have a long natural history of between 10 and 35 years. It is estimated that the annual conversion rate of a polyp to a cancer is approximately 0.25%.

So if you have a colonoscopy and you remove a pre cancerous polyp, you have almost a zero chance of that polyp turning cancerous.

The bad news is if you have one polyp, there is a much higher chance you will get another one (in this small high risk group, the chance of a second polyp over 7 years was 30 percent)..

There is a graph at the NYTimes article that won’t replicate that shows the actual chance of a person getting cancer of the large intestine goes down is from 1.5% to 0.75 % over a 20 year period if you do a colonoscopy.

The graph also shows that most of the cancers were found ten years or more after the colonoscopy was done.

This is both good and bad news.

Some doctors are suggesting that everyone get a single colonoscopy at age 60 as a screening test for bowel cancer. If a person passes, they don’t need another one. But if they have a polyp, they need to be checked again in a couple years to see if they have  new polyp.

This study suggests that to find all the cancers, you need a test every ten years.
Problem: There aren’t enough docs trained in the procedure to do this. And although the risks of the procedure is small, it isn’t zero..From EMedicine:

The 60-cm flexible sigmoidoscope has greater range than the rigid sigmoidoscope, which, at best, only reaches the distal sigmoid (20 cm). A double-contrast barium enema study detects most colon tumors (80-95%); however, flexible sigmoidoscopy should precede the barium enema, as it is more accurate in detecting small rectal lesions. The double-contrast barium enema has a low perforation rate (1 in 25,000).

Colonoscopy detects more adenomatous polyps than a barium enema, and polyps can be excised during the procedure. Colonoscopy is approximately 3 times more expensive, has a much higher perforation rate (1 in 1700) than barium enema, and fails to reach the cecum in 5-30% of patients.

That last part is a problem: One technical problem with a colonoscopy is that even in the best of hands, the doctor might not be able to get the tube all the way to the start of the large intestine (the cecum) and miss a cancer, and one technical problem with the barium enema is that it misses polyps in the last ten inches, near the rectum, so you need to do a shorter tube exam to check the rectum.

This brings me to a strange fact about cancer of the large intestine: Fifty years ago, we had many many more cancers in the rectum, so a simple rectal exam could pick up many of them. Now we find more of them “upstream”, where it takes more sophisticated tests to find. So why has the cancer pattern changed? Is it due to the change in the American diet to lower amounts of animal fats (e.g. lard) and more fiber? And could a high fiber diet prevent the cancer? What about NSAIDs (or aspirin) lowering the cancer rate here? Lots of arguments about this in the literature.
Then there is the problem of race: This may not be racism per se, but let’s face it: There are few friendly neighborhood clinics in the inner city where you know doc from church and the nurses live down the street. So people tend to use the local Emergency room as their doctor.

And in small town USA, there is a chronic physician shortage and a colonoscopy might mean traveling to the “nearby” city (40 miles for us in Oklahoma) to get the test.

So there you have it: We have a test that if done often enough could eliminate cancer of the large intestine, but it’s expensive, there is a complication rate high enough that you wouldn’t want to do it on  low risk patients, and there simply aren’t enough doctors to do it on everyone every ten years, which is what would be needed to eliminate the cancer.

And it’s a test that patients hate.

So what is needed is a better screening test…maybe a blood test to check who needs the colonoscopy, and then do the colonoscopy more often on these “high risk” patients.

But if you have symptoms, or have a family member who has had either colon polyps or bowel cancer, it would be worth while for you to have a colonoscopy.

And the rest of you? It might be worth it too. Ask your doctor.


Nancy Reyes is a retired physician living in the rural Philippines.

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