Colonoscopy panned for routine screening
New Canadian guidelines say colonoscopy should not be used for routine screening to detect colorectal cancer in patients with no symptoms or family history of the disease.
Instead, the guidelines from the Canadian Task Force on Preventive Health Care strongly recommend that low-risk patients aged 50 to 74 be screened using fecal occult blood tests every two years or sigmoidoscopy every 10 years.
Sigmoidoscopy involves the insertion of a flexible scope to view the lower portion of the colon and rectum rather than the entire tract, as is the case with colonoscopy.
The task force also advises against screening asymptomatic patients age 75-plus because of their reduced life expectancy and the lack of research showing benefit or potential harms of the tests.
Task force member Dr. Scott Klarenbach of the University of Alberta says the guidelines do not apply to high-risk patients who have symptoms or a family history of the disease.
Colorectal cancer is the second most common cause of death from cancer in men and the third leading cause of cancer deaths in women. In 2015, an estimated 25,000 Canadians were diagnosed with colorectal cancer, and about 9,300 died from the disease.
“Although colonoscopy may offer clinical benefits that are similar to or greater than those associated with flexible sigmoidoscopy, direct evidence of its efficacy from randomized controlled trials” in comparison with other screening tests is “lacking,” said Dr. Maria Bacchus, an internist at the University of Calgary who chaired the guideline working group.
“However, ongoing clinical trials are working to address this research gap,” she said.
The task force, which bases its advice on the latest available results from clinical trials, strongly recommends stool- based testing or sigmoidoscopy for adults aged 60 to 74, but its recommendation is weaker for those 50 to 59.
“And that’s only because the incidence — that is the number of people with cancer — changes with age,” said Klarenbach.
“For those who are over the age of 60, the incidence of cancer goes up dramatically and they’re more likely to have a larger absolute benefit from screening,” he said. “But many people who are younger, over the age of 50, they might decide after discussion with their primary-care provider that they would like to get screened as well.”
One reason for the weak recommendation for screening patients aged 50 to 59 is that a small percentage of fecal blood tests can provide false- positive results, which can cause anxiety as well as the need for a followup test — typically a more invasive colonoscopy, said Klarenbach.
“You’re less likely to pick up real disease because it’s less common ( in that age group). Whereas, when you’re a little bit older, you still have that false- positive risk but you’re going to pick up much more disease.
“So it’s weighing those risks and benefits.”
The Canadian task force was established to develop clinical practice guidelines for primary-care providers related to a variety of preventive-health issues, based on a systematic analysis of the most recent scientific evidence. The guideline is available at www.canadiantaskforce.ca.