Colonoscopy exams get a bad rap.

Even though such exams are brief and painless, many people fear and avoid them. Roughly one third of Americans for whom the exams are recommended are not getting them.

Yet colonoscopy is one of the most effective of all cancer prevention methods. As many as 60% of colon cancer deaths could be prevented if everyone 50 years old or above underwent colonoscopies, according to the Centers for Disease Control and Prevention (CDC). (Current recommendations call for screening to begin at age 45.)

In fact, a study by a team of researchers from Dana-Farber, Brigham and Women’s Hospital, and the Harvard School of Public Health found that people who received either a colonoscopy or a sigmoidoscopy, which allow doctors to look inside the large intestine through a thin tube and snip away at precancerous growths, had a markedly lower rate of cancers in the rectum and lower colon than did other patients.

“Colonoscopies are the most sensitive test since they examine inside the entire colon for cancer or polyps,” says Jeffrey Meyerhardt, MD, MPH, clinical director of the Gastrointestinal Cancer Center at Dana-Farber Cancer Institute. “These polyps are precursors for cancer that, if removed, will not turn into cancer.”

The recommendations for colonoscopy screening aren’t changed by a recent European study that seemed to call into question the exam’s ability to reduce colorectal cancer deaths, Dana-Farber specialists say. The study found that among people who were offered a colonoscopy, the exam lowered the risk of developing colorectal cancer by 18% but didn’t reduce the risk of dying from the disease. These statistics, however, overlook the fact that only 42% of those who were offered a colonoscopy actually got one. Among those who did have a colonoscopy, the risk of developing the disease was reduced by 31% and the risk of dying from it decreased by 50%.

“The take-home message is therefore that colonoscopy screening for colorectal cancer works, but only if you actually do it,” says Dana-Farber’s Kimmie Ng, MD, MPH. “Further follow-up of the clinical trial results is needed, as well as comparisons with other screening tests, and dedicated efforts to improve adherence to recommended screening guidelines.”

When should I have my first colorectal cancer screening?

Previously, and in many parts of the world, health authorities recommended that most individuals have their first colonoscopy at age 50. But a rise in colorectal cancer rates in younger people has prompted a U.S. federal task force to recommend that screening begin at age 45 — or earlier for some patients with high-risk conditions.

“A concerning increase in colorectal cancer incidence among younger individuals has been documented since the mid-1990s, with 11% of colon cancers and 15% of rectal cancers in 2020 occurring among patients younger than 50 years, compared with 5% and 9%, respectively, in 2010,” Ng wrote in an editorial in JAMA accompanying the article about the guideline changes. Ng is the director of the Young-Onset Colorectal Cancer Center at Dana-Farber.

As a result, the U.S. Preventive Services Task Force (USPSTF) now recommends the following:

• Adults ages 45 to 75 should be regularly screened for colorectal cancer.
• Adults ages 76 to 85 should discuss with their doctor whether they should be screened. Since colorectal cancer is a slow-growing disease, the risks and benefits of screening after age 75 should be weighed against the individual’s overall health, life expectancy, and prior screening history. Adults in this age group who have never been screened for CRC are more likely to benefit, especially if they are healthy enough to undergo treatment if colorectal cancer is detected.

How often should I be screened?

For most patients, if a colonoscopy is normal, it should be repeated every 10 years. If one or two low-risk polyps are found and removed during the exam, the next colonoscopy should be done in five years.

If a colonoscopy detects precancerous polyps or the patient has factors associated with a higher risk of colorectal cancer, the physician may recommend that colonoscopies be repeated more frequently. People at increased risk include those with:

• A personal history of colorectal cancer or adenomatous polyps
• A personal history of ulcerative colitis or Crohn’s disease
• A family history of colorectal cancers or polyps
• A known inherited hereditary colorectal cancer syndrome (such as familial adenomatous polypsis (FAP) or Lynch syndrome)

What does a colonoscopy involve?

A colonoscopy is considered the gold standard screening test for colorectal cancer. It requires the patient to adhere to a cleansing regimen of a liquid diet and laxatives the day before the procedure, which is done in a clinic or hospital, usually under sedation. The doctor passes a long, flexible tube with a light and camera through the anus and along the entire length of the colon, which is about five feet. The tube is then withdrawn, and the physician examines the walls of the colon for any abnormal growths such as polyps, or tumors.

Polyps can be removed using instruments that snip them off; they’re then sent to a laboratory for analysis. Removing precancerous polyps can prevent the development of cancer; colonoscopies and sigmoidoscopies are the only procedures in which this is possible.

Because of the sedating drugs, the patient usually doesn’t feel any pain and remembers little or nothing about the procedure. Because of the drugs used, however, someone must accompany the patient on the return home, and resting for the remainder of the day is recommended.

Are there alternatives to a colonoscopy?

Among the options are a sigmoidoscopy, which is similar to a colonoscopy but is limited to the lower part of the colon. Because sigmoidoscopies are less extensive, they don’t require as much prep as colonoscopies, Meyerhardt says.

An alternative screening procedure is a “virtual colonoscopy,” a specialized type of CT scan that does not require any instrument to be inserted into the colon and can be done without sedation. However, there is radiation exposure from the CT scan, and it requires the same type of bowel cleansing preparation as a conventional colonoscopy, and if abnormal growths are detected, a colonoscopy would need to be performed.

There are several types of stool-based screening tests that involve a sample collected at home and analyzed in a laboratory. They are not diagnostic tools (in other words, they cannot diagnose colorectal cancer), and a positive test needs to be immediately followed by a colonoscopy. Such stool tests need to be done more often than a colonoscopy. A positive test result of a stool-based test always calls for a follow-up colonoscopy and biopsy.

Types of stool-based tests include:

• Fecal occult (hidden) blood testing, in which patients complete a set of stool samples at home and send them to be tested for evidence of blood. This could indicate bleeding from fragile vessels in a polyp or tumor. The test should be done annually.
• Fecal immunochemical test (FIT), which also looks for blood in the stool. It, too, must be done every year.
• Multitargeted stool DNA test, which in addition to looking for occult blood, can identify abnormal segments of DNA from a tumor or polyp and can also detect DNA mutations in certain genes associated with colorectal cancer. The only such test available in the United States is Cologuard, which should be done every three years.

“All of the screening tests carry some risks, and the more sensitive the test, the higher the risk,” says Meyerhardt. “During a colonoscopy, there’s a very small risk of a perforation of the bowel, bleeding, or infection. The biggest risk of fecal occult blood testing and other screening measures is missing something, which could turn out to be much more serious.”

Is it safe to be screened for colon cancer during COVID-19?

Don’t let COVID-19 keep you from your regular health checkups, regular screenings included. Health care providers and facilities, including Dana-Farber, have taken many precautions to protect patients that come for visits as well as procedures, like colonoscopies.

To learn how your provider is protecting you during the pandemic, you should contact their office. Learn more about what Dana-Farber is doing to protect patients and staff.