Colorectal Cancer Screening

Despite Advances in the Accuracy of CT Colonography in Detecting Polyps, Digestive Health Experts Urge Patients to Consider Risks and Realities



BETHESDA, Md., Oct. 5 - New research from the University of Wisconsin comparing optical colonoscopy to CT colonography published in the New England Journal of Medicine today raises several important issues for the public about colorectal cancer screening using a CT scan of the abdomen. "Gastrointestinal physicians are committed to preventing colorectal cancer, and to advancing new frontiers in medicine.
While all of us on the front lines of battling colorectal cancer will
welcome effective and clinically proven new tools, the evidence needs to be
closely evaluated and patients need to recognize that a virtual test is not
without significant potential risks in its own right," commented Dr. David
Johnson, M.D., FACG, President of the American College of Gastroenterology.

The Wisconsin study in today's NEJM compared CT colonography (CTC)
performed for screening in 3120 adults with primary optical colonoscopy
(OC) in 3163 similar consecutive adults. A major limitation of the study
was it was not randomized, patients chose their preferred screening method.
Referral for polypectomy during optical colonoscopy was offered for all
polyps detected by CT colonography of at least 6 mm in size. Patients with
one or two polyps in the range 6 to 9 mm were offered the option of
follow-up surveillance by CT colonography. The researchers do not report
whether CTC identified smaller polyps, which would routinely be removed
according to established practice guidelines because it is impossible to
reliably identify which small adenomas will become cancerous.

CTC and OC found similar rates of advanced neoplasms and cancers. About
8 percent of CTC screenings resulted in referrals for OC for removal of
suspicious polyps. The total numbers of polypectomies in the CTC and OC
groups were 561 and 2434, respectively, so far more potentially cancerous
polyps were removed by colonoscopy. Seven perforations occurred in the OC
group during screening, and none occurred in the CTC group.

According to Dr. Johnson, "The nonrandomized design of this study is
problematic. The higher rate of cancer in the OC group suggests that the
study populations were different, and a higher percentage of patients in
the OC group might have received previous negative screening test results
-- such testing would select for a lower rate of cancers and advanced
adenomas in the colonoscopy group and potentially bias to higher detection
in the CTC cohort. Also, the rate of perforation in the colonoscopy arm was
twice what is expected in a screening population. Thus, we need additional
information to interpret this nonrandomized comparison before we can
generalize the results to clinical practice."


Evaluating the Potential of CT Colonography - What Patients Should Know

When evaluating new potential screening technologies, including CT
colonography, the ACG has focused its evaluation on several pieces of
evidence including: sensitivity for identification of polyps of various
sizes, standards for polyp removal, correlating patient risks (in this case
from radiation exposure), frequency of exams and the economic impact to the
healthcare system of separate diagnostic and therapeutic exams.

An important reality of CT colonography is the likelihood that patients
will need a follow-up with optical colonoscopy. Of the patients undergoing
CT colonography in the University of Wisconsin study published in NEJM, 7.9
percent were referred for optical colonoscopy for removal of potentially
pre-cancerous polyps at least 6mm in size. Earlier findings by Dr.
Pickhardt and his colleagues in 2004, at least 30 percent of patients
undergoing virtual colonoscopy required conventional colonoscopy to remove
polyps 6mm or larger.

ACG notes that the CTC technology requires the same bowel preparation
as optical colonoscopy. There is also evidence that due to the insertion of
a tube in the rectum and insufflation of the abdomen with air or gas, the
patients, who are not sedated and awake tend to feel discomfort. In
addition, the fact that some percentage of patients will be required to
follow up a CT colonography with a therapeutic or, in cases where there the
CT results are not clear, a second diagnostic colonoscopy, has patient
acceptance and economic implications.

"Patient acceptance is another key factor in evaluating the promise of
a new technology. The fact that patients undergoing optical colonoscopy are
sedated and do not experience pain in association with the procedure and
they will be able to have an examination and any necessary therapeutic
intervention in a single visit will be important in evaluating which test
is best for a particular patient," added Dr. Johnson.

It is important for patients to understand that no guideline group,
including the American Cancer Society or the Multi-Society Task Force on
Colorectal Cancer has yet endorsed CT colonography as appropriate for
colorectal cancer screening.

According to the American College of Gastroenterology, colonoscopy
remains the best test and the current gold standard for colorectal cancer
screening and prevention. Three studies have shown that colonoscopy
prevents about 80 percent of colorectal cancers from developing by removing
pre-cancerous polyps. "The public should recognize that there is no
evidence that any radiographic test, including CT colonography prevents the
development of colorectal cancer," said Dr. David Johnson.

"There is a tremendous body of evidence that shows that clearing the
colon of polyps, including small polyps, significantly reduces colorectal
cancer mortality. Because of its excellent sensitivity in detecting polyps
and its potential for removing them and breaking the sequence of polyp to
cancer in a single diagnostic and therapeutic intervention, colonoscopy is
one of the most powerful preventive tools in clinical medicine. Until a
radiographic test can meet that standard, gastroenterologists will continue
to champion the lifesaving potential of colonoscopy," Johnson added.



SOURCE American College of Gastroenterology