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06/28/17

Colorectal cancer screening can save lives – so why don’t more Canadians do it?

Colon cancer is the second-most common cancer in Canada, and the second-leading cause of cancer death in the country, estimated to have killed 9,300 Canadians in 2016 alone.

Yet a simple screening test can not only detect cancer but also prevent cancer from developing by identifying pre-cancerous polyps which can then be removed before they turn cancerous. That’s far better than breast or prostate cancer screening tests, where evidence remains weak or divided on their value.

While mammograms have become routine, data from colorectal cancer screening programs across the country show many Canadians still aren’t taking advantage of simple, at-home screening tests.

At the same time, those whose screening returns a positive result often wait longer than is recommended for a follow-up colonoscopy.

Data from the 2014 Canadian Community Health Survey show that only 48 to 68 percent of eligible individuals were considered up-to-date for colorectal cancer screening.

The Canadian Task Force on Preventive Healthcare recommends a fecal test every two years for individuals aged 50 to 74 who are at average risk of developing colorectal cancer. Flexible sigmoidoscopy, which uses a scope much like a colonoscope, but examines only the rectum and lower colon, is also recommended as a screening tool, to be repeated every 10 years. Those with increased risk – including people with a family history of colon cancer – are encouraged to undergo screening by colonoscopy. Abnormal stool screening tests must be followed by a colonoscopy to make a definitive diagnosis.

Colonoscopies are not recommended as a screening tool in those at average risk of developing colorectal cancer because they’re expensive, time consuming and can be risky – one in 1,400 may result in bowel perforation and the sedative can sometimes trigger reactions or lead to complications.

Screening participation figures fall dramatically when considering data provided by organized screening programs, which do not capture colonoscopies conducted outside the program. In 2013-2014, they reported that the percent of eligible individuals who had a fecal test ranged from 8.6 percent in Newfoundland & Labrador to 53 percent in Manitoba.

For now, it’s difficult to get a true picture of screening participation, as provincial screening programs started at different times and were at different stages of roll-out or development when the most recent figures were collected.

Still, with less than half of eligible Canadians participating in screening programs, experts are searching for ways to overcome barriers to colorectal screening.

“It’s not the most attractive of prospects whether by collecting stool samples or by having a colonoscopy. I think it’s low on people’s priorities and, perhaps, also low on their health care provider’s priorities as well,” says David Armstrong, a gastroenterologist in Hamilton who is also president of the Canadian Association of Gastroenterology and chair of the National Colorectal Cancer Screening Network.

“I think it’s just a little bit of the yuck factor,” adds Clarence Wong, a gastroenterologist in Edmonton and the Provincial Medical Lead for the Alberta Colorectal Cancer Screening Program. “It’s great to talk about breast cancer; we’ve normalized that discussion. But here you’re talking about poop tests. It’s just not as sexy to talk about that.”

Two types of fecal screening

Fecal tests look for a microscopic component of blood, which can be a predictor of polyps and cancer lesions, since they are more easily damaged than healthy tissue and will release trace amounts of blood during the passage of feces.

There are two tests available to detect the presence of blood, including the fecal occult blood test (FOBT) currently used in Ontario and Manitoba, and a fecal immunochemical test (FIT), currently available in all other provinces, including New Brunswick and Quebec, which are still implementing province-wide programs.

Ontario will transition to FIT testing in 2018, says Catherine Dubé, an Ottawa-based gastroenterologist and the Clinical Lead for Ontario’s ColonCancerCheck program.

That’s in line with a recommendation made in a 2012 Auditor General’s report, which noted screening numbers had plateaued at 53 percent. It noted a survey conducted by the Ontario Ministry of Health & Long-Term Care found that 37 percent of physicians believed the FOBT was not reliable enough to be used as a population-based screening tool.

The FOBT is considered to have a high “ick” factor, and to be tedious for users, who must avoid foods that are thought to interfere with the test’s results, collect stool samples for three consecutive days, and smear them on a card to be sent to the lab for testing.

FIT uses a different technology to identify blood, requires only one stool sample, has no dietary restrictions and is considered more accurate and better able to detect polyps and early stage cancers because it detects hemoglobin of colonic origin.

The FIT test has also been found to increase screening participation. A 2013 study by researchers in Portland, Oregon conducted a patient survey that indicated FIT was less unpleasant, more convenient and easier to complete than FOBT.

For someone with a positive screening stool test, the target is to have a colonoscopy performed within eight weeks or 60 days of a positive result; however, wait times vary considerably across Canada, with many waiting twice as long as recommended, ranging from 104 to 151 days.

It raises the question about whether the system can handle higher screening participation and the additional colonoscopies that would be needed if participation rates were to increase.

Prioritizing potential cancers in colonoscopy queues

Armstrong says there are two factors at play in colonoscopy wait times: part of it is capacity, but part of it is the organization of how colonoscopies are scheduled.

About 970,000 colonoscopies are performed each year in Canada but only about 15 percent of them are for cancer screening purposes. By comparison, the number of colonoscopies performed annually in England is about 550,000 for a population of about 53 million.

“One could argue that colonoscopy may be underperformed in England but a roughly three-fold difference, per capita, suggests that there may be overutilization in Canada,” Armstrong says.“This may be due to excessively frequent colorectal cancer screening or surveillance, screening in patients who do not need it and investigation of symptoms, such as abdominal pain, constipation, for which the yield is low.”

“Mammogram was built for screening but colonoscopy has so many other uses than screening,” Wong says, including exploring causes of abdominal pain, bleeding or bowel problems.

The trick is finding ways to move patients with positive screens higher up the wait lists while still balancing the need for diagnostic testing for other patients, something Wong says is easier done with FIT tests. FOBT gives only a positive or negative result for the presence of blood. FIT measures how much blood, which can be an indicator of more advanced polyps and adenomas, or benign tumours.

FIT tests are quantitative, meaning they can determine the exact nanograms of blood per sample. In Alberta, Wong has set the test’s cut off rate at 75 nanograms of blood – anyone with that amount of blood or higher in their sample will be considered to have a positive result. In British Columbia, the cut off rate has been set at 100 nanograms.

Wong says calibrating the test’s sensitivity allows provinces to better control the flow of patients needing follow-up testing.

Colonoscopies take some planning and preparation for patients: people need someone to drive them to and from the procedure, they must flush their bowel in advance of the procedure, and some with conditions like diabetes or high blood pressure or those who use anticoagulants, will need to consult with their doctors to ensure that the procedure can be safely performed.

Provinces must also be prepared for colonoscopies prompted by FIT-positive tests to require more skill and take more time, as they’re more likely to reveal advanced polyps.

Wong says greater participation in screening programs may sound like more burden on the system, but it can also help balance the demand for colonoscopy by removing average risk people with negative screening from the colonoscopy queue – particularly in places like Ontario, where colonoscopies can be performed at private clinics.

“That puts the right person in line at the beginning,” Wong says.

Reducing barriers

Besides the “ick” factor, those who treat colorectal cancer say there’s a multitude of reasons people don’t pursue screening, despite its success rate. In places where people must request an at-home screening kit from their pharmacist or family doctor, some in the 50-79 target group are too embarrassed to ask, or may not even know about the possibility of screening.

Others fear what they may find.

“Finding a cancer is not a death sentence,” Armstrong says. Screening can prevent cancer by identifying polyps before they turn cancerous so they can be removed during a colonoscopy. The cure rate for early stage colorectal cancer is more than 90 per cent.

Some feel the screening is a hassle – collecting a stool sample is enough to turn people away, but the threat of a follow-up colonoscopy sends even more over the edge.

“Neither is as bad as they think,” Armstrong says. “It’s a nuisance to sit down and collect stool and put it on card and send it off. But there are worse things in life. It’s a small price to pay for avoiding the second most frequently diagnosed cancer in Canada.”

Dubé says the greatest predictor of whether a patient will undergo colorectal screen is their primary care provider’s attitude about the test.

“If GPs [or nurse practitioners] believe in it and promote it, their patients are more likely to complete it,” she says.


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Source: http://healthydebate.ca/2017/06/topic/colorectal-cancer-screening-colonoscopy