Jan. 28, 2008 (Orlando, Fla.) -- 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.
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 have 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.