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Blood Test May Warn of Colon Cancer

Study Shows Test Detects Cancer in Time to Remove Precancerous Growths
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WebMD Health News

June 15, 2007 - A new blood test promises advance warning of colon cancer -- in plenty of time to find and remove precancerous growths.

The test detects either of two chemical markers abundant in colon cancers. The markers, dubbed colon-cancer-specific antigen-3 (CCSA-3) and CCSA-4, are also abundant in colon polyps that are well on their way to becoming colon cancers -- but appear to be rare in benign polyps and in other tissues.

Somehow, these markers find their way into the bloodstream, where they can easily be detected and measured. The leader of the team that found the markers and developed the test is Robert H. Getzenberg, PhD, professor of urology, oncology, pharmacology, and molecular sciences at Johns Hopkins University in Baltimore.

"Currently there are no blood tests for colon cancer. This would significantly change how people with colon cancer are detected," Getzenberg tells WebMD.

In preliminary studies, Getzenberg and colleagues tried out the test on 107 people undergoing routine screening colonoscopy, 28 people known to have colon cancer, and 125 people with various kinds of colon polyps or other cancers.

The test was 100% sensitive for colon cancer -- that is, it didn't miss a single patient. It was about 90% sensitive for identifying people who had either colon cancer or advanced adenomas (growths almost certain to become colon cancers).

The test was 82% to 91% specific, meaning that up to 18% of the time the test gave false-positive results in normal people and in people with benign polyps and other noncancerous growths.

"The goal here, the way we would use this, is to identify people who really need a colonoscopy," Getzenberg says.

Findings 'Exciting but Early'

Durado Brooks, MD, MPH, director of prostate and colorectal cancers for the American Cancer Society, doesn't agree that the test should be used in that way. Brooks, who was not involved in the Getzenberg study, notes that everyone who tests positive on the blood test would need a colonoscopy -- but what about those who test negative? Should they get a colonoscopy at some future time point, or a repeat blood test?

"At this point, we have to look at whether this has value as a standalone screening option," Brooks tells WebMD.

Brooks calls the new findings "very encouraging, but very early." He points out that the test still has to be validated in a large number of unselected people. Indeed, Getzenberg says such a study already is under way, with 500 people enrolled at several different institutions.

"In about two years we should have this thing out there," Getzenberg says.

Brooks hopes Getzenberg is right. However, he points to a possible problem with the test.

"The Hopkins data is a little concerning in that 16% of those with cancers other than colon cancer had a false-positive result," Brooks says. "That means that anyone who had a positive result on this test but a negative colonoscopy would have to embark on a tumor search. That would raise the price tag -- and the anxiety level -- for those who have false-positive test results."

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