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Colon
cancer screening:
Risk stratification at the core
of Canada's new guidelines, access variability taken into consideration
By
Diana Swift
Banff,
AB—Colon cancer screening guidelines, developed
by the Canadian Association of Gastroenterology and the Canadian
Digestive Health Foundation, were presented at Canadian Digestive
Diseases Week by Desmond Leddin, MB, Head, Division of Gastro-enterology,
Dalhousie University, Halifax, NS.
“The guidelines are aimed at the public as well as healthcare
professionals,” said Dr. Leddin, who with Richard Hunt, MD,
Professor of Medicine, McMaster University, Hamilton, ON, co-chaired
the cross-Canada committee of 11 practitioners that shepherded the
guidelines through 15 drafts. “As you are aware, the public
is deservedly agitated about this issue and needs guidance about
appropriate investigation.”
The committee’s objective was to provide guidance to Health
Canada, while not making sweeping, one-size-fits-all recommendations
that disregard widely differing screening resources among practices.
“We wanted the guidelines to respect the fact that access is
variable.”
Risk stratification is at the core of the guidelines.
Colon cancer is uncommon before age 50, with risk rising notably
after that. Individual history of IBD or polyps, and family history
(whether it be a case of a first- or second-degree affected relative
or multiple affected relatives) also increase susceptibility.
Dr. Leddin stressed that average-risk screening involves asymptomatic
patients. “Investigation for rectal bleeding or a change in
bowel habits is not screening, but rather diagnostic workup.”
Under the Canadian guidelines, which are in line with the U.S. and
U.K. positions, an asymptomatic person younger than 50 years with
a negative family history needs no screening. “I know many
of you are screening people under age 50, but this is generally
not an effective use of resources.”
Asymptomatic persons 50 or older with a negative family history
are considered at average risk and should undergo screening with
a tool to be determined by the physician’s judgment, patient
preference, scientific evidence and, of course, available resources.
Options for screening such individuals are:
• FOBT every two years;
• Flexible sigmoidoscopy every five years;
• Flexible sigmoidoscopy plus FOBT every five years;
• Double-contrast barium enema every five years; and,
• Colonoscopy every 10 years.
Colonoscopy’s superior sensitivity and specificity allow for
longer intervals between tests.
At age 50, even those with negative family histories become vulnerable.
“At that point we need organized provincial programs to deal
with the average-risk population. The screening tools need to be
decided at the provincial level based on the realities of life in
the particular province,” said Dr. Leddin, conceding that,
in some venues, even an FOBT screening program would be difficult.
For individuals at higher-than-average risk, the algorithm becomes
more complicated. These include people with genetic syndromes, a
finding of polyps on colonoscopy, and a positive family history,
with risk rising according to the numbers and degrees of relatives
affected.
“Some of the most common referrals we get in Halifax are patients
with a family history of one first-degree relative of less than
60 years who developed colon cancer,” he said. Also frequent
are referrals for an affected first-degree relative over age 60.
“Patients with a mom of dad with colon cancer in their seventies
are a very common source of referral.”
Patients with an affected first-degree relative under age 60 may
have a
genetic defect that tends to emerge earlier in successive generations,
so these individuals need screening. Like the American, the Canadian
guidelines advise screening these candidates beginning at age 40,
or 10 years earlier than the youngest affected relative’s age
at colon cancer onset. “Here we recommend colonoscopy as a
screening tool, not flexible sigmoidoscopy or barium enema. This
is an appropriate way to deploy that resource,” he said.
Individuals with a first-degree relative affected after age 60 are
considered at average risk, but their screening should begin at
age 40. “Many of you, I know, would be uncomfortable here because
average-risk screening would include FOBT for a person whose parent
developed colon cancer in his seventies.”
In the case of people with two or more first-degree relatives affected
at any age, the recommendation is colonoscopy every five years beginning
at age 40 or 10 years younger than the youngest age at diagnosis
of polyps or cancer in the family—whichever comes first.
As for individuals with one second- or third-degree relative with
colon cancer, the scientific data and both the American Gastroenterological
Association and the British Society of Gastroenterology support
average-risk screening beginning at age 50.
If polyps are found, the recommendations are as follows:
One to two tubular adenomas of less than 1 cm warrant a repeat colonoscopy
only in five years. “We have a tendency—myself included—to
scope people too often. And I admit I’m nervous when I find
a polyp and say, ‘I don’t need to see you for five years.’
I know this technology is not perfect and may miss some lesions.
I worry about the medical-legal side if the patient comes back with
an invasive lesion. And the patients themselves tend to press you
to shorten the interval. But resist that temptation. If you stretch
out the interval, particularly for low-risk polyps, you will improve
access for other patients and your yield will be better when you
actually do the scope,” Dr. Leddin said.
If more than two adenomas are found, it may be that the mucosa is
unstable, and current data indicate that repeat colonoscopy in three
years is appropriate.
In the case of numerous polyps, advanced adenomas and malignant
or large sessile polyps, the guidelines recommend colonoscopy after
a shorter interval to be determined by the physician’s clinical
judgment. “We don’t want to be too prescriptive here.
There’s room for latitude. Colonoscopy should be customized
according to clinical appearance, anxiety level, and patient preference.”
In the case of hereditary nonpolyposis colorectal cancer, the guidelines
recommend colonoscopy every one to two years, beginning at age 20,
or 10 years younger than the earliest case in the family, whichever
comes first. With familial adenomatous polyposis (FAP), the recommendation
is annual sigmoidoscopy, starting at age 10 to 12. For attenuated
adenomatous polyposis coli (AAPC), the guidelines prescribe annual
colonoscopy beginning at 16 to 18 years of age. “AAPC is like
FAP, but the polyps appear first in the proximal colon, so sigmoidoscopy
is not appropriate. These patients will develop right-side cancer
while the rectum looks normal,” said Dr. Leddin, who has several
AAPC families in his practice.
Looking ahead, he noted that genetic testing and stool-based assays
could be marshalled to ease the burden of colon cancer screening.
“Virtual colonoscopy may play a screening role; this seems
like a promising filter to me,” he said, referring to a December
2003 New England Journal of Medicine study in which only 10 to 13
per cent of those undergoing virtual colonoscopy needed to go on
to optical colonoscopy. Another option to ease the screening burden
is alternate providers. Evidence is mounting, for example, that
trained RNs can be efficient physician extenders in flexible sigmoidoscopy.
Prevention
“Unfortunately, we have backed off on the issue of nutrition
as a tool for changing mass health. But we need to look at preventing
the burden of disease as opposed to detecting it once the horse
is out of the barn,” Dr. Leddin said.
Far from stopping at producing a document, the guideline group plans
to activate a public awareness campaign on screening and to work
with provincial gastroenterology associations to provide data and
facilitate their dealings with provincial health ministries in establishing
programs.
“We recommend that you do not try to set up a screening program
at your hospital. You will be overwhelmed and you’ll drive
yourself into the dust trying to negotiate resources with the government,”
he said. “The responsibility for this major public health issues
lies squarely with the provincial governments.”
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