A large study that examined the effect of colonoscopy screening on the risks of colon cancer and related deaths fueled doubts about the procedure's benefits. However, some physicians say that the findings should be interpreted carefully.
The study published in the New England Journal of Medicine included 84,585 presumptively healthy people aged 55-64, drawn from population registries in Poland, Norway, Sweden, and the Netherlands.
Of those, 28,220 people were invited to undergo a single screening colonoscopy (the invited group), while the rest did not receive an invitation (the usual-care group). Less than half of the invited group — 11,843 (42.0%) — got a colonoscopy. The median follow-up of participants was ten years.
Authors of the study say colonoscopy screening for colon cancer prevention is not as effective as previously believed because the risk of the disease decreased only by 18% among the participants who were offered colonoscopy screening. Moreover, there was no significant difference between the groups in terms of mortality.
Points out to limitations of the study
In response to the study that made the headlines last week, the American Cancer Society (ACS) released a statement saying that it's "hard to know the value of a screening test" when most of the participants in the study did not get screened.
"However, study patients who did undergo a colonoscopy had a 31% decrease in the risk of colorectal cancer as compared to those who were not screened. This result points to the value of continued screening," Dr. William Dahut, a chief scientific officer at the ACS, said in the statement.
Dr. Louise Emilsson, a docent at the Department of Medical Epidemiology and Biostatistics at Karolinska Institute in Sweden and one of the study authors, says that it is important to perform randomized studies in a population similar to the population in which the intervention will be implemented.
"Randomizing individuals from the total population to screening or no screening is a relevant study design to assess the potential effect of a nationwide screening intervention," she said to Healthnews.
Dr. Benjamin Schmidt, a gastroenterologist based in St. Louis, Missouri, says that even though there was not a statistically significant difference in colon cancer deaths between the groups, the findings are not as profound as it sounds due to the study's limitations.
He points out that among 42% of patients who were invited to a colonoscopy and had one, the mortality from colon cancer decreased dramatically — by 50% compared to those who did not get a colonoscopy.
"The polyp detection rates for the doctors performing the colonoscopies for this study were lower than the typical standards that the US uses. A screening test like colonoscopy is only as good as the people performing it," Schmidt said to Healthnews.
Moreover, Schmidt says, a 10-year follow-up is not long enough for monitoring cancer development, as data from at least 15-20 years are necessary.
Alternatives are less effective for some
Asked why less than half of the invited people showed up for colonoscopy, Emilsson says that many patients without any symptoms might have thought the procedure was too invasive. Moreover, it requires bowel preparation and sedatives for many patients.
A colonoscopy is an exam used to look for changes in the colon and rectum. During the procedure, a long, flexible tube (colonoscope) with a tiny video camera at the tip is inserted in the rectum. In the US, the test is recommended for colorectal cancer screening in those 45 and older.
Given the results of our study, Emilsson thinks that colonoscopy should not be the first-line recommendation for general population screening. At the same time, a fecal blood test or sigmoidoscopy, a similar procedure that examines the lower part of the colon, are relevant alternatives.
"However, if you have a high family risk or other risk factors for colorectal cancer, you should definitely do a colonoscopy screening."
Schmidt says that he would recommend colonoscopy to his patients, as it is "the gold standard colon cancer screening test" because it can identify not only cancer but also small polyps before they become cancer. While stool tests and CT (computed tomography) colonography are also effective, they are not as sensitive or specific at identifying colon cancer or polyps.
"This means they are more likely to miss cancer and polyps or more likely to be positive in the absence of cancer or polyps. Colonoscopy has the benefit of being able to both detect and treat polyps — if any of these alternative screening methods are positive, the patients will then require a colonoscopy to identify and remove any polyps that are present," he said.
However, colonoscopy does not come without risks. One of the most severe complications of the procedure is endoscopic perforation of the colon, which has been reported at a rate of 0.03-0.7%.
Emilsson says that in their study, no perforations and 15 major bleedings after polyp removal were reported; therefore, the risk of major complications is low.
"I do think benefits are small in the general population as reported in our study, so I would say it is up to the patients themselves to decide if it is worthwhile, but for those at higher risk of colorectal cancer, potential benefits definitely outweigh the small risk of the procedure," she said.
According to the Centers for Disease Control and Prevention, the risk factors for colon cancer are:
- Inflammatory bowel disease such as Crohn’s disease or ulcerative colitis.
- A personal or family history of colorectal cancer or colorectal polyps.
- A genetic syndrome such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (Lynch syndrome).
Certain lifestyle factors, such as lack of regular physical activity, a low-fiber or high-fat diet, overweight and obesity, alcohol consumption, and tobacco use, may also contribute to an increased risk of colon cancer.