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Too Few
Get Colon Cancer Screening
Virtual Colonoscopy Not Ready for
Widespread Use
April
29, 2004 – One of the most dreaded events of aging are regular
colonoscopies and senior citizens were closely watching the development
of "virtual colonoscopy," a less invasive and safer method of detecting
colon cancer. A new study warns, however, this method “may not be ready
for widespread use.” But, there still may be reason for hope.
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Too Few
Americans Getting Colon Cancer Screening
Too few Americans are getting
screened for colon cancer, even though most doctors say they
are recommending the procedures to patients over age 50. A
study published in Cancer Epidemiology, Biomarkers and
Prevention compared patient medical records of screening
with a survey of doctors' recommendations and found a large
gap between the two.
Researchers from Baylor College
of Medicine studied a large Texas medical practice with 284
doctors and around 200,000 patients. They examined the
records of 214 patients who had been with the practice at
least a year and who were 53 or older. Though more than 80%
of doctors in the practice said they advised patients over
age 50 to be screened, only half of the patients studied had
actually gotten a test for blood in the stool, and only
one-third had had a sigmoidoscopy or colonoscopy.
Colon cancer is the third
leading cause of cancer death among men and women in the
United States. Screening can catch the disease at an early
stage, when it is easier to treat, or prevent it entirely.
The American Cancer Society recommends that people at
average risk for the disease begin screening at age 50,
while those at higher risk should begin even earlier.
"If we could get the patient
[screening] rates up to what physicians say they
[recommend], that would be great in reducing mortality from
colon cancer," said lead researcher Sarah Hawley, PhD, an
assistant professor in the Department of Family and
Community Medicine. |
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This
study found substantial variations in virtual colonoscopy accuracy.
After comparing virtual colonoscopy with standard colonoscopy in several
hospitals, the researchers found that the virtual procedure missed many
precancerous polyps and even some cancers.
"The
main result of this study was surprising and disappointing," wrote Peter
Cotton, MD, in the Journal of the American Medical Association
this month (Vol. 291, No. 14: 1713-1719). Cotton is director of the
Digestive Disease Center at the Medical University of South Carolina, in
Charleston, and was principal investigator for the study.
According to
background information in the article, conventional colonoscopy is the
best available method for detection of colorectal cancer and its
precursors. However, it is invasive and not without risk, so a simpler
alternative would be welcome, certainly by senior citizens. Computed
tomographic colonography (CTC) has been reported to be reasonably
accurate in the diagnosis of colorectal tumors in studies performed at
expert centers. CTC involves the examination of computer-generated
images of the colon constructed from data obtained from an abdominal
computed tomographic examination.
Previous studies have suggested that virtual colonoscopy is comparable
to standard colonoscopy, finding more than 90% of lesions in the colon.
But those studies were all conducted in single hospitals by radiologists
who were highly experienced with the technique.
The
new study was conducted in 9 different hospitals by radiologists who
were required to have performed at least 10 similar procedures
previously.
"An
obvious question is whether the radiologists in our study were
sufficiently experienced [with the procedure]," said Cotton. "Our
results indicate that [virtual colonoscopy] is not ready for routine use
at this time, as many others have concluded."
Virtual
Procedure Less Than Half as Effective
Cotton and his colleagues compared the procedures in 615 patients.
First, a radiologist performed virtual colonoscopy, which uses a
computed tomography (CT) scanner to create images of the colon. Then a
gastroenterologist administered conventional colonoscopy, which involves
inserting a long, lighted tube into the colon to examine it with a small
video camera.
In a
side-to-side comparison, standard colonoscopy detected 99% of polyps 6mm
or larger (103 of 104), while virtual colonoscopy detected only 39% (41
of 104). Standard colonoscopy detected 100% of polyps 10mm or larger (42
of 42), while the virtual colonoscopy found only 55% (23 of 42). Virtual
colonoscopy also missed 2 of 8 cancers detected by conventional
colonoscopy.
The
accuracy of virtual colonoscopy varied widely between hospitals. One
hospital that had a lot of experience with virtual colonoscopy had an
82% detection rate using this technique, but at the other 8 hospitals,
the combined detection rate was just 24%.
These
findings suggest that doctors who perform this procedure must be highly
trained and experienced if they are to do it successfully.
"The
differences between what virtual colonoscopy can do and what it will do
if applied in ordinary practice circumstances are so great that
physicians must be cautious," wrote David Ransohoff, MD, of the
University of North Carolina, Chapel Hill, in an accompanying editorial.
Still Too Early
for Screening Use
Because virtual colonoscopy is less invasive than standard colonoscopy,
it has been touted as having the potential to increase the persistently
low levels of colon cancer screening in the US.
Only
about half of the people who should be screened for this deadly cancer
actually do so. Yet screening can detect colon polyps before they become
cancerous, or find cancer in its earliest stages, when it is easier to
treat. Colon cancer is the second leading cause of cancer death in the
US.
"I
hope our study will stimulate more studies on improving technique,
software, scanners and training so that virtual colonoscopy will
eventually provide an accurate, noninvasive screening tool," said
Cotton. "If virtual colonoscopies are improved so they are as effective
as the conventional colonoscopy, many more people would get screened,
and more precancerous lesions would be detected."
Currently, patients must endure the same bowel cleansing preparation for
both procedures, and if virtual colonoscopy does find a suspicious
polyp, conventional colonoscopy is still needed to remove it.
Virtual colonoscopy could gain an edge, Cotton said, if techniques can
be developed to eliminate the bowel preparation and simplify the process
of interpreting the computerized images of the colon.
The
American Cancer Society currently recommends that people at average risk
for colon cancer begin screening at age 50. People are encouraged to
have one of several tests, including traditional colonoscopy, flexible
sigmoidoscopy, double contrast barium enema, or testing for blood in the
stool.
In an accompanying
editorial, David F. Ransohoff, M.D., of the University of North
Carolina, Chapel Hill, writes that "as the study by Cotton et al
suggests, the biggest near-term problem for virtual colonoscopy is that
it may be implemented too widely without sufficient regard for current
technological problems that affect sensitivity.
"The level of
sensitivity and specificity that virtual colonoscopy can achieve, in
some specialized situations, is known. Yet the differences between what
virtual colonoscopy can do and what it will do if applied in ordinary
practice circumstances are so great that physicians must be cautious.
There are many important steps yet to be taken in learning how to
implement this new technology appropriately," he writes. |
