Recent study provokes controversy about the effectiveness of colonoscopy as a screening test
Earlier this month, controversial news headlines emerged: “Colonoscopies have a lower-than-expected benefit in preventing colon cancer, with no reduction in colon cancer mortality”, “Disappointing results on colonoscopy benefits”, creating confusion about the study and whether colonoscopies are an effective screening test. Let’s explore the study.
The NordICC trial included average-risk individuals between the ages of 55-64 years old from several European countries who were not experiencing any symptoms of colorectal cancer. Participants were randomly assigned to:
a) Receive an invitation to undergo a single screening colonoscopy,
b) Not receive any invitation to undergo a screening colonoscopy.
Of all the participants that received an invitation to undergo a colonoscopy, only 42% accepted the invitation and underwent screening.
At 10-year follow-up, the risk for developing colorectal cancer was as follows:
a) 0.98% in the “intention-to-screen” population, i.e. the participants who received an invitation for single screening colonoscopy,
b) 1.2% in the control population – the participants who did not receive any invitation for single screening colonoscopy
These findings show a significantly lower relative risk (18%) of developing colorectal cancer among participants who received an invitation to undergo a colonoscopy.
The risk for colorectal cancer-related death was:
a) 0.28% in the intention-to-screen population,
b) 0.31% in the control population
The difference in risk of for colorectal cancer-related death was not statistically significant.
An important concern among experts in the field is that the actual title of the study is misleading in and of itself: “Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death”, and that’s because the study is not actually looking at the effectiveness of colonoscopy, but rather, how effective an invitation to undergo screening by colonoscopy is at reducing the risks of CRC and related death.
The study findings show that sending out an invitation to undergo single screening with a colonoscopy is not very effective – while it did seem to reduce the risk for CRC, it did not decrease CRC-specific or all-cause mortality (death) compared to people who did not receive any invitation. An important factor to consider is that only 42% of participants who received an invitation went forward with a colonoscopy. In other words, less than half of individuals who were invited to get screened actually did it, which demonstrates that uptake of colonoscopy at the population-level is low. This does not mean that colonoscopy is not an effective screening test at reducing the risk of colorectal cancer and related death.
The bottom line is that colonoscopies remain the gold standard for colorectal cancer detection. Though they may not be the optimal primary screening test at the population level for average-risk individuals, (which is why in Canada the fecal immunochemical test (FIT) is recommended as the first screening test for individuals at average risk), colonoscopy continues to be the most sensitive test for detecting colorectal cancer as a follow-up test or primary screening test for high-risk individuals.
Participating in colorectal cancer screening helps to catch the cancer in earlier stages when it is most treatable. In Canada, the colorectal cancer screening guidelines are as follows for average-risk individuals between the ages of 50-74 years:
• Have a stool test (FIT) every 2 years. In the case of a positive stool test, follow-up should be done with a flexible sigmoidoscopy or colonoscopy, or
• Flexible sigmoidoscopy every 10 years
(Canadian Task Force on Preventive Health Care, 2016)
Talk to your family doctor to find out more about participating in colorectal cancer screening. Get in touch with us at firstname.lastname@example.org for more information about screening.
Remember that the best screening test is the one that gets done!