Lost In Translation In RCT Colonoscopy Study: Some Kind Of Colorectal Cancer Screening Is Essential To Lower Mortality Rates

Headlines are meant to grab your attention. So, if you read yesterday that “colonoscopy does not reduce risk of death from colorectal cancer” that may have caused a jolt. Haven’t we been conditioned to believe that colonoscopy is a rite of passage for middle aged folks?

The media headlines were based on results published in the New England Journal of Medicine from a first-of-its-kind large and randomized trial. The study suggests the benefits of colonoscopies for cancer screening of low-risk, asymptomatic people are overestimated. The 10-year study marks the first time colonoscopies have been compared head-to-head to no cancer screening in a randomized trial.

The study may have people wondering whether they should get the procedure. Much more problematically, the snippets people hear about the study on the news, in social media, and elsewhere, may have them questioning whether they should get screened at all. Nonetheless, while colonoscopy may not be the gold standard it’s been made out to be, one or more colorectal cancer screening tools are essential to detect cancer and lower mortality rates.

Unpacking the study

A 2014 comprehensive literature review revealed that “there is no available evidence from RCTs supporting the efficacy of colonoscopy as a colorectal cancer screening test.” So, using a RCT methodology, the newly released landmark study sought to test the effect of colonoscopy screening on the risks of both colorectal cancer and related deaths. Findings over a 10 year period indicated that colonoscopies for colorectal cancer screening did not have a statistically significant impact on the risk of cancer deaths.

Nevertheless, in the trial, the risk of colorectal cancer at 10 years was 18% lower among participants who were invited to undergo screening colonoscopy than among those who were assigned to no screening. Also, only 42% of patients randomized to colonoscopy completed the test. Among patients who actually got the colonoscopy, there was a 31% decrease in colorectal cancer and a 50% decline in mortality.

What the study doesn’t say

Colorectal cancer is the third leading cause of cancer-related deaths in men and in women in the U.S.. It’s projected to cause more than 52,000 deaths this year. Colorectal cancer screening is a vital tool to reduce the incidence of cancer deaths. And, this doesn’t just apply to at-risk people. Low-risk, asymptomatic people benefit from being tested.

In a 2021 study published in the Lancet Oncology researchers found that since the year 2000 colorectal cancer incidence and mortality declined more in European countries with long-standing fecal test, sigmoidoscopy, or colonoscopy screening programs, than in countries with more recently implemented or no large-scale programs.

Furthermore, in the U.S. and Europe, the mortality rates of colorectal cancer have been in a long-term decline. A variety of screening tools used in the U.S. and Europe appear to have played an important role in reducing mortality rates of colorectal cancer.

Invariably, there has been confusion regarding colon cancer screening tools, in part because there are so many options. Some, including flexible sigmoidoscopy and the fecal immunochemical test (FIT), have more RCT-supportive evidence than others. Flexible sigmoidoscopy is a procedure in which a trained medical professional uses a flexible, narrow tube with a light and tiny camera on one end to look inside a person’s rectum and lower colon. A sigmoidoscopy is less invasive than a colonoscopy, because it only examines the lower part of the colon, while a colonoscopy looks at the entire large intestine. Sigmoidoscopy is generally recommended once every five years, while a colonoscopy is recommended once every 10 years. Both sigmoidoscopy and colonoscopy can detect and remove polyps.

The FIT test is the least-invasive screening for colon cancer. It tests for hidden blood the stool, which can be an early sign of cancer. This test only detects blood from the lower intestines. A newer version of the FIT test also detects altered DNA in the stool. Depending on the type of FIT test, it is recommended once every one to three years.

Long before the RCT study on colonoscopies was published, the FIT tests or flexible sigmoidoscopy were first line colorectal cancer screening tools for low-risk, asymptomatic adults ages 50 to 74 in many countries, including, among others, France, the Netherlands, Norway, Sweden, Denmark, Italy, Spain, U.K., Israel, and South Korea.

The testing guidelines disseminated in the U.K. and European Union have consistently favored screening tests being introduced into routine healthcare only after their effectiveness has been proven in randomized trials. As a result, only sigmoidoscopy and guaiac-based FOBT (or the modern version, FIT) are currently recommended for routine use across most of Europe.

Concerning the use of colonoscopy as a screening method, the only countries outside the U.S. that advise it are Switzerland, Germany, and Austria. Interestingly, cancer death rates in Austria and Germany have declined even more rapidly than other European countries with alternative screening programs in place. Whether this has anything to do with more extensive use of colonoscopy hasn’t been investigated.

Closer to home, the Canadian Task Force on Preventive Health Care, cites two preferred colon cancer screening methods for low-risk, asymptomatic adults ages 50 to 74:

• Fecal occult blood testing (FOBT or FIT), every two years;
• Flexible sigmoidoscopy, every 10 years

On the other hand, the U.S. Preventive Services Task Force (USPSTF) recommends a range of colon cancer screening methods for low-risk, asymptomatic adults 50 to 74, without, however, ranking them in terms of their strength of evidence. Essentially, the USPSTF guidelines provide equally strong recommendations for all five tests:

• High-sensitivity guaiac FOBT or FIT every year; DNA-FIT every 1 to 3 years;
• Computed tomography colonography every 5 years;
• Flexible sigmoidoscopy every 5 years;
• Flexible sigmoidoscopy every 10 years plus annual FIT;
• Colonoscopy screening every 10 years.

The USPSTF states that “clinicians and patients may consider a variety of factors in deciding which test may be best for each person.” In reality, for a large and growing portion of the population once-a-decade colonoscopies have superseded the use of testing alternatives.

Still, more than a quarter of the U.S. adult population between 50 and 74 has not been screened at all for colorectal cancer. There’s an attendant risk that the media headlines knocking colonoscopy off its pedestal will misinform Americans on the need to get tested for colorectal cancer. In fact, they could deter Americans from getting checked at all for colorectal cancer.

Perhaps study results like these should come with a disclaimer of sorts. Clinicians can and should debate the benefits of colonoscopy screening versus other methods. But, screening for colorectal cancer is indispensable, whether in the form of a colonoscopy or a less invasive tool.