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Addressing
Canada's high incidence of colorectal cancer
By
Diana Swift
TORONTO,
ON--With an estimated 19,200 new cases of colorectal
cancer and 8,400 CRC deaths in 2004, Canada has one of the world's
highest incidence rates of this lethal disease. "This is the
Number One cause of non-tobacco-related cancer death in men and
women, and it has a higher fatality rate than either breast or prostate
cancer," Linda Rabeneck, MD, MPH, told attendees at the first
Ontario Gastrointestinal Multidsciplinary Oncology Conference.
The life risk of developing CRC is about equal in men (6.3 per cent)
and women (5.6 per cent). In Ontario this high-burden disease accounts
for more hospital bed days of occupancy than any other cancer.
The majority of CRC cases are sporadic: six per cent are associated
with important but uncommon genetic syndromes such as FAP and HNPCC
and one per cent with inflammatory bowel disease. In 15 per cent
of cases there is an associated family history. "About 95 per
cent of cases arise through the pathway of benign adenomatous polyps
that turn malignant," said Dr. Rabeneck, Head, Division of
Gastroenterology, Sunnybrook & Women's College Health Sciences
Centre, Toronto.
"Since the malignant process take at least 10 years, in colorectal
cancer we have an opportunity to detect and remove lesions at the
precancerous stage-unlike breast cancer, where mammography detects
the calcifications of early cancer." Nearly 30 per cent of
individuals aged 50 have at least one adenomatous polyp.
Over the past decade, mounting evidence has supported the role of
screening to reduce CRC rates, with the strongest evidence coming
from randomised controlled trials of fecal occult blood testing.
Three RCTs have found that FOBT followed by colonoscopy for positive
cases results in a 15 to 33 per cent reduction in CRC mortality.
Case-control studies have shown a reduction in mortality associated
with sigmoidoscopy and cohort studies have shown a reduction in
CRC incidence with colonoscopy and polypectomy.
In 2001, The Canadian Task Force on Preventive Health Care updated
its recommendations and advised that all persons aged 50 and older
of average risk be screened for CRC with annual or biennial FOBT
or flexible sigmoidoscopy every five years (CMAJ 2001;165:206-8).
"Screening should now be the standard of practice in primary
care," Dr. Rabeneck said.
Selby's case-control study of screening sigmoidoscopy found that
this safe, non-sedative-requiring, easy-prep office procedure could
reduce mortality from CRC in the rectum and distal colon by up to
60 per cent (NEJM 1992;326(3):553-57). Some have argued, however,
that sigmoidoscopy is like "doing mammography on just one breast,"
she said.
For negative flexible sigmoidoscopies, the cancer miss rate is only
one to two per cent. In 1999, Ontario gastroenterologist Ted Shapero,
MD, established a successful nurse-delivered FS screening program
that has shown CRC detection rates similar to physician-operated
programs (Can J Gastro 2001;15:441-45).
In Britain, baseline data from the U.K. Flexible Sigmoidoscopy (FS)
Screening Trial of more than 40,000 subjects suggest a cancer detection
rate of 3.5 cancers per 1,000 people screened (Lancet 2002;359:1291-1300).
That 0.3 per cent slightly exceeds the 0.2 per cent detection rate
reported in the first round of an RCT of FOBT screening (Hardcastle
et al, Lancet 1995;348:1472-77), suggesting that endoscopy may detect
cancer earlier than FOBT. "Some 62 per cent were Duke's A in
the UK FS Trial compared with 46 per cent in the FOBT trial,"
she said, "and 12 per cent versus 0.8 per cent of adenomas
were detected by FS versus FOBT, respectively."
In the case of colonsocopy, no large RCTs have been published. The
cohort investigation undertaken by the U.S. National Polyp Study,
however, showed a reduction of CRC incidence of up to 90 per cent
compared with the estimated incidence in SEER (Winawer et al,
NEJM 1993;329:1977-81). In this study, a large number of men
and women with a mean age of 61 years underwent colonoscopy plus
polypectomy with periodic follow-up colonoscopy.
The Veterans Affairs Co-Operative Study Group, led by David Lieberman,
MD, studied just over 3,000 asymptomatic, mainly male veterans aged
50 to 75 years (mean, 63 years). It found at least one adenomatous
polyp in over one-third, and advanced neoplastic lesions (adenomas
10mm+/villous/ high-grade dysplasia/invasive cancer) in 10.5 per
cent (NEJM 2000;343(3):162-68). "Thirty of the 3,000,
or one per cent, were found to have actual cancers on screening
colonoscopy. But it's not entirely fair to compare that with the
FS 0.3 per cent detection rate because the study populations were
different," Dr. Rabeneck noted.
Based on his findings for polyps, Lieberman estimated that just
under one-quarter of those with advanced neoplasms would have tested
positive on FOBT, and about 70 per cent would have been detected
with FS. If both modalities are combined in a one-time screening,
Lieberman found that the detection rate is a little better: 75.8
per cent (NEJM 2001;345(8):555-60), missing less than one-
quarter of those with advanced neoplasms.
Despite national and provincial endorsements of population-based
screening programs, Dr. Rabeneck noted that Ontario is still limited
to "opportunistic and ad hoc screening" triggered by word-of-mouth
or TV publicity about celebrities. "We do not have an organized
screening program, which would entail widespread public messaging
and invitations to screening, timely access to endoscopic procedures,
quality assurance around endoscopic procedures and follow-up, as
well as tracking of outcomes."
Dr. Rabeneck's recent Ontario study of 982,443 screen-eligible men
and women aged 50 to 59 years reported very low estimated rates
of endoscopic and non-endoscopic large-bowel testing (Am J Gastro
2004;99(6):1141-44). Between January 1, 1995, and December 31, 2000,
approximately six per cent underwent colonoscopy or sigmoidsocopy
(flexible/rigid); 14.5 per cent had non-endoscopic testing such
as FOBT or barium enema; and 79.5 per cent had no testing. "So
we know that the extent of large-bowel screening for cancer is less
than 21 per cent since these figures include tests done for all
reasons, both screening and diagnostic."
While no Canadian province has an organized CRC screening campaign,
the U.K. is currently embarking on a population-based program and
has completed an FOBT pilot study.
In a recent Ontario pilot study, Dr. Rabeneck noted that a random
sample of 20 Ontario hospitals showed that seven of 134 new cases
of CRC were screening-detected; leaving 95 per cent detected because
of symptoms. "We don't need one more breakthrough in medical
science to make a huge impact on CRC incidence. We've had the tools
for decades, and for one decade we've had good strong evidence that
these tools work. We just need to apply them," she said.
Adequate screening depends, of course, on capacity, she added. Examining
patterns of use over the past few decades, Ontario's Institute for
Clinical Evaluative Studies (ICES) noted that, in men, colonoscopies
more than doubled per 10,000 50-to-74 year olds since 1997, while
barium enemas have and flexible sigmoidoscopies have declined. Colonoscopy
rates in women approach those in men. About six per cent of men
undergo FOBT.
Accessibility
ICES also found that in 2001 the 67 smallest Ontario hospitals did
far more colonoscopies than the province's two largest facilities
per 100 total weighted cases. The giant Hamilton Health Sciences
Centre and Toronto's University Health Network did only 9,000 procedures
compared with the 25,000 done by the smallest centres. "That
quantifies what we already know: that we have a tough time finding
resources for screening when our focus is cancer treatment not prevention,
when it's priority programs such as organ transplants and not screening,"
she said.
"The hospital-based
endoscopy model is designed not for screening but for treatment,
so our model doesn't fit."
She noted that access to colonoscopy increases if you live in a
rural area because of the larger volume handled by smaller hospitals.
Access is also increased for people in the highest economic quintile.
"So colonoscopy
access is a huge issue. Its delivery is currently constrained and
uneven and we need to rethink how we finance, organize and deliver
this service. Whatever the initial screening tool-FOBT, sigmoidoscopy
or barium enema, all positives have to proceed to colonoscopy."
In Ontario, the Task Force on Endoscopy, chaired by Dr. Rabeneck,
is currently seeking solutions and, in a project funded by the Change
Foundation, is developing a training program for nurse endoscopists.
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