A colonoscopy study has some wondering if they should have the procedure. What you should know

By Elizabeth Cohen, CNN Senior Medical Correspondent

A new European study on colonoscopies — the largest of its kind — has complicated results, and it’s left some people wondering whether they should have the procedure to screen for colon cancer.

“I think the most important message is that colon cancer screening is effective, and you should get screened,” Dr. Jason Dominitz told CNN. He’s the national director of gastroenterology for the Veterans Health Administration, and he co-authored an editorial that accompanies the study in The New England Journal of Medicine.

In a colonoscopy, a doctor inserts a long, flexible tube into the rectum. A tiny video camera at the end of the tube allows the doctor to see the inside of the colon. They look for precancerous polyps and cancerous growths, as well as any other abnormalities, and they can cut out tissue that looks suspicious and have it biopsied.

Doctors do colonoscopies when someone has symptoms of colon cancer, and they do them to screen for colon cancer in someone who doesn’t have symptoms. There are other methods of screening for colon cancer, such as checking for hidden blood in the stool, but if something looks suspicious in those tests, doctors often then recommend a colonoscopy.

“Colonoscopy is ultimately the test that’s done to evaluate for colon cancer,” Dominitz said.

Dominitz helped CNN sort through the findings of this new study to see what it means for you. Spoiler alert: Colonoscopies save lives!

What did this new study show about the effectiveness of colonoscopies?

In this study, about 12,000 people in Sweden, Poland and Norway got colonoscopies. They saw a 31% reduction in their risk of colon cancer and a 50% reduction in their risk of dying from colon cancer compared with people who were not invited to get a colonoscopy.

Was that about what would be expected?

Some US studies have suggested that colonoscopies are even more effective. One study followed nearly 90,000 health care professionals for 22 years. Some of them chose to receive a screening colonoscopy, and some did not. The researchers estimated that screening colonoscopy was associated with a 40% reduction in the risk of getting colon cancer and a 68% reduction in the risk of dying of colon cancer.

Why would there be different success rates in the three European countries compared with the US?

Dominitz says one reason might be that most people in the European study didn’t have sedation when they got their colonoscopies. Only 23% of the patients in the European study received sedation, but virtually everyone having a colonoscopy in the US gets it. Colonoscopies can be uncomfortable, and doctors might, without even realizing it, be less thorough if people are in pain. Thoroughness — getting the scope into the folds and crevices of the colon — is important for finding growths called polyps. The more polyps doctors are able to find, the more they can reduce the person’s risk of being diagnosed with or dying from colon cancer.

Bottom line: Should you still get screened for colon cancer?

Yes! Generally speaking, you should start getting regular colonoscopies at age 45. For people who are at high risk because of a family history or other factors, it’s even younger; see these recommendations from the US Centers for Disease Control and Prevention and the American Cancer Society. And screening doesn’t have to involve a colonoscopy. There are other tests, too, but colonoscopy is the most common.

In the European study, people were invited to get colonoscopies. Why would they have to be invited? Isn’t colon cancer screening standard practice in those countries?

Only recently have Sweden, Poland and Norway started screening their populations for colon cancer. Their programs started about 2015, and in the study, people were invited to have a screening colonoscopy from 2009 to 2014. The patients were then followed for about 10 years to see if they developed colon cancer.

How many of the study participants said yes to the invitation to get a colonoscopy?

In the European study, 28,000 people ages 55 to 64 were invited to get a screening colonoscopy. Only 42% said yes.

Why so few?

Dominitz thinks it’s in part because people in those countries were not accustomed to the idea of getting screening colonoscopies. They hadn’t had them before, and their friends and family probably hadn’t, either. Also, at the time of the study, there was no campaign to encourage colonoscopies — no Katie Couric (or Ryan Reynolds) to raise awareness about colon cancer.

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CNN’s Naomi Thomas and Justin Lape contributed to this report.