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Do You Really Need That Colonoscopy?

Health experts say routine screenings are key to cancer prevention and early detection

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The death rate for colorectal cancer — one of the most common and deadly types of cancer in the United States — has been declining for decades. And health experts largely credit routine screenings for the dramatic drop.

After all, as we know, cancers are easier to treat the earlier they are found. Regular screenings also help doctors spot and remove problematic polyps before they have the chance to progress into cancer.  

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But a recent study that has garnered much public attention has called into question the effectiveness of a common type of colorectal cancer screening: the colonoscopy. More than 15 million are performed in the U.S. each year.

Results from a large, first-of-its-kind trial published Oct. 9 in the New England Journal of Medicine found that colonoscopies only lowered the risk of colorectal cancer by a modest 18 percent in study participants invited to get one, and that the reduction in the risk of death from the cancer that was discovered was not significant. Many experts, however, are urging caution when it comes to interpreting the results, and a big reason has to do with the way the study was designed.

7 warning signs of colon cancer

• Blood in the stool (this could look dark brown or black)

• Rectal bleeding

• Change in bowel habits

• Unexplained weight loss

• Cramping or abdominal pain

• An urge to have a bowel movement when the bowel is empty

• Weakness or fatigue

Source: American Cancer Society

The team of European researchers randomly divided nearly 85,000 adults between the ages of 55 and 64 into two groups: One group was asked to get a colonoscopy, the other was not. And among those participants asked to get the test, only 42 percent opted for it. The researchers then compared the number of colorectal cancers and deaths from the disease in each group over a 10-year period.

“So you're talking about a comparison where [more than] half the people in the intervention group didn't actually have the actual intervention,” says Jeffrey Meyerhardt, M.D., chief clinical research officer at Dana-Farber Cancer Institute in Boston.

In a statement, William L. Dahut, M.D., chief scientific officer for the American Cancer Society, argued, “It’s hard to know the value of a screening test when the majority of people in the study didn’t get it done.” He pointed out, however, that study participants who did have a colonoscopy had a 31 percent decrease in the risk of colorectal cancer compared to the group that didn’t get screened. The risk of death was also cut by about 50 percent.

“This result points to the value of continued screening,” Dahut said.

Another caveat is that the study’s follow-up period was roughly 10 years, says Ashwani Rajput, M.D., director of the Johns Hopkins Sidney Kimmel Cancer Center. And the benefits of screening are more obvious over time, he adds. The study’s authors plan to repeat their analysis at 15 years, so the results could change.

Finally, it should be noted that previous colonoscopy studies have shown a much greater risk reduction in both colorectal cancer incidence and death; so have studies evaluating other colorectal cancer screening methods.


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“It should not be interpreted that colonoscopies aren't helpful. And most importantly, it should not be interpreted that there's not a benefit to colon cancer screening,” Meyerhardt says.

Bottom Line: Get screened and stay up to date on screenings

Despite headlines touting disappointing study results, experts say colonoscopies and colorectal cancer screenings, more generally, absolutely saves lives and shouldn’t be skipped. “There's no question that colorectal cancer screening works,” says Carole Macaron, M.D., a gastroenterologist at Cleveland Clinic, who points out that this latest study was really trying to assess the effectiveness of a colonoscopy as a public health intervention when it's being offered to a large group of people.

If you are at average risk for colon cancer — meaning you don’t have a family history of the disease or another condition that increases your chances of getting it, like Crohn's disease — routine screenings should start at age 45 and continue to 75. Whether you should continue screenings from age 76 to 84 is a decision you should make with your doctor. Adults 85 and older don’t need to be screened.

A colonoscopy is just one type of colorectal cancer screening. During this procedure, the doctor looks at the entire length of the colon using a flexible tool that has a camera attached at the end. One of the benefits to this screening is that if your doctor spots a polyp during the procedure (these are small clumps of cells that can be precancerous), they can take it out on the spot.

“If left inside 10, 15 years down the road [a polyp] could progress to cancer, so you want to remove them so that technically your risk of cancer from that polyp turns into zero,” Macaron says. If you opt for the colonoscopy, you should have it done every 10 years. If the test uncovers polyps your doctor might ask you to repeat the test sooner.

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Other colorectal cancer screening options include a sigmoidoscopy, which is similar to a colonoscopy except the doctor only looks at a portion of the colon, and a CT colonography (or virtual colonoscopy), which takes images of the colon. Both of these options require more frequent screening than the colonoscopy; they should be done about every five years.

There are also screenings that you can do at home and send to a lab or your doctor’s office for analysis. These stool-based tests — which should be done every one to three years, depending on the type of test you choose — can detect blood or altered DNA in the stool, both of which raise red flags for cancer. It’s important to note that if your results from any of the alternative screenings come back abnormal, you will need to get a colonoscopy.

Not sure which screening to choose?

Talk to your doctor. There are pros and cons to each, and one might work better for your situation. “What matters is getting screened,” Macaron says. “That’s the endpoint.”

Still, millions of Americans aren’t getting tested. According to the Centers for Disease Control and Prevention (CDC) about 30 percent of adults ages 50 to 75 are not up to date on colorectal cancer screenings; roughly 20 percent have never been screened. And the pandemic has likely caused these percentages to grow, since the number of Americans getting screened for cancer in general has dropped dramatically as a result of COVID-19.

Meyerhardt’s advice: Don’t delay your colorectal cancer screening, whichever one you choose to get. “Catching people at later stages increases the likelihood that patients will not be cured of their cancer or will have a higher chance of their cancer coming back,” he says.

If caught early, the five-year survival rate for colorectal cancer is about 90 percent.

Questions to ask your doctor

Do I need to get a screening test for colorectal cancer?

• Am I at increased risk for colorectal cancer?

• What screening test(s) do you recommend for me?

• How do I prepare?

• What’s involved in the test? Will it be uncomfortable or painful?

• Is there any risk involved?

• How long do I need to wait for results?

• Will I need someone with me for the test?

Source: Centers for Disease Control and Prevention

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