Virtual or Real, Colonoscopy Is Best

Virtual colonoscopy is nearly as accurate
as the real thing, and both methods far outperform three other standard
screening methods for colon cancer , German researchers report.

Their study of more than 300 low-risk, healthy men and women compared
virtual and real colonoscopy to flexible sigmoidoscopy, fecal occult blood test
(FOBT ), and immunological
detection of hemoglobin in stool (FIT).

The researchers say the study is the first to look at how the five screening
techniques perform, alone and in combination, in the same patient.

"What we found," says University of Munich's Frank Kolligs, MD,
"is that for relevant lesions, virtual colonoscopy probably performs
equally well to colonoscopy."

The other three methods are far less accurate, carrying a high rate of
false-negative and/or false-positive readings -- even when combined, he
says.

"The bottom line," Kolligs tells WebMD, "is that if you do
colorectal cancer screening, you should have a test that allows
the doctor to visualize the colon."

Colonoscopy vs. Other Colon Cancer Screens

In a colonoscopy, doctors guide a thin, flexible tube with a tiny camera
through the patient's entire colon to check for abnormalities. Doctors consider
it the gold standard for detecting polyps that can lead to colon cancer as well
as for the cancer itself.

But many people avoid the procedure because of discomfort and a small
risk of complications.

In the past few years, virtual colonoscopy, more accurately known as CT
colonography or CTC, has begun to catch on. It uses special software to view CT
scans of a patient's colon. Kolligs says it, too, allows doctors to see colon polyps before they become deadly colon
cancers.

Flexible sigmoidoscopy is similar to colonoscopy, but it only examines the
lower third of the colon. Not surprisingly, that means it can miss a large
number of polyps, says Richard Schilsky, MD, a specialist in gastrointestinal
cancers at the University of Chicago.

Both FOBT and FIT look for hidden blood in the stool. Occult, or hidden,
blood can be an early sign of colon cancer.

Kolligs says that doctors thought FIT, which directly measures a component
of blood called hemoglobin in the stool, would prove more accurate than FOBT,
which indirectly measures hemoglobin. But that didn't prove to be the case.

Colonoscopies, Real and Virtual, Outperform Other Tests

The study, presented at the annual Gastrointestinal Cancers Symposium,
involved 307 men and women aged 50 or older. None had symptoms of colon cancer.

After stool samples were collected for FIT and FOBT testing, the patients
underwent colonoscopy and CTC on the same day. By counting lesions found in the
lower third of the colon in a colonoscopy, the researchers could approximate
the results of sigmoidoscopy.

Results showed that colonoscopy and virtual colonoscopy detected advanced
adenomas -- growths destined to become cancers -- at nearly the same rate. They
also detected polyps larger than 10 millimeters -- a size considered dangerous
-- at basically the same rate. Colonoscopy found far more tiny polyps -- 5
millimeters or smaller -- than did CTC. But such polyps only rarely turn
cancerous.

Sigmoidoscopy, on the other hand, only found about two-thirds of colon
growths. FIT detected fewer than half of growths, while FOBT only found about
one-fifth.

FOBT gave false-positive results to 10% of people who didn't have the
dangerous growths. The comparable figure for FIT testing was 14%.

Kolligs says that combining the results of various tests -- sigmoidoscopy
plus FOBT, sigmoidoscopy plus FIT, and FOBT plus FIT -- resulted in "no or
only slightly increased rates of detection over one test alone."

Schilsky says that while his institution has virtual reality as an option
for patients who might prefer not have a colonoscopy, he still recommends his
patients ave the real thing. The reason, he tells WebMD, is that any polyps
that are found via colonoscopy can be immediately removed. Patients who have
suspicious polyps found by CTC must still undergo colonoscopy to have them
taken out.

By Charlene Laino
Reviewed by Louise Chang
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