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    Blood Test Might Spot Colon Cancer
By Alan Mozes

HealthDay Reporter
TUESDAY, Oct. 25 (HealthDay News) -- A simple blood test could be an accurate, easy way to spot colorectal cancer early, a team of American and German researchers report.

The novel blood analysis technique identifies patients with elevated levels of an abnormal form of the adenomatous polyposis coli (APC) gene, a warning sign of malignancy.

The blood test appears to be 100 percent effective in screening patients with advanced stage colorectal cancer, while researchers were able to identify early-stage disease in more than 60 percent of cases. The technique was not, however, good at isolating signs of noncancerous tumor growth.

"One of the challenges is to try and design tests to detect early tumors, and we have shown that abnormal forms of the APC gene can actually be found in the blood of patients with cancer -- even in those with early cancers who presumably could be cured by surgery alone," said study co-author Dr. Bert Vogelstein, of the Howard Hughes Medical Institute and The Sidney Kimmel Comprehensive Cancer Center at The Johns Hopkins Medical Institutions, in Baltimore.

According to the American Cancer Society, colorectal cancer is the third most common cancer among American men and women. The organization estimates that more than 145,000 new cases will be diagnosed in the United States in 2005, resulting in more than 56,000 deaths.

Standard screening procedures for colon cancer include stool tests that search for small samples of hidden blood; flexible sigmoidoscopy, in which doctors use a long, video-equipped tube to examine the lower half of the colon for signs of cancer; and colonoscopy, where doctors use a longer device to scan the entire colon.

A barium enema procedure -- involving the expansion of the colon for better X-rays -- is another screening option.

For men and women of average risk over the age of 50, the ACS recommends either yearly stool exams, a flexible sigmoidoscopy once every five years, or both. Alternatively, patients are encouraged to undergo a barium enema once every five years, or a colonoscopy once every 10 years.

Although colonoscopy is effective in spotting cancerous or precancerous growths, the procedure can be uncomfortable, with patients usually requiring sedation.

Compared to colonoscopy, a reliable, minimally invasive test would be ideal. Looking for such a screen, Vogelstein's team noted that over 85 percent of colorectal tumors at all stages of development produce abnormal APC genes. They speculated that mutated APC might prove a good marker for colorectal disease.

Between 2003 and 2005, the American-German team collected blood samples from 33 male and female German colorectal cancer patients over the age of 50. Ten additional healthy patients within the same age range were also sampled as a control group.

Six of the cancer patients had late-stage malignancies, while 16 patients had early-stage tumors. The remaining 11 patients had large, benign tumors, known as adenomas.

Blood analyses revealed abnormal DNA fragments of the APC gene in all six of the advanced stage cancer patients, the researchers report in this week's online edition of the Proceedings of the National Academy of Sciences. Similar mutant fragments were also observed in samples from nearly two-thirds of the early-stage cancer patients.

In contrast, abnormal APC was found in the blood of just one patient with benign tumors.

Based on the findings, the researchers concluded that the APC blood test is most effective in diagnosing patients with late-stage colorectal cancer. It might also be effective in spotting many -- if not all -- earlier stage cancers, they said. The test is not likely to be useful in spotting premalignant growths, however.

"Colonoscopy is the gold standard, and this blood test is clearly not as sensitive," said Vogelstein. "On the other hand, you could argue that most patients don't get colonoscopy for various economic, medical or social reasons, so most patients go unscreened. Hopefully, this will give patients other options."

"This also goes -- potentially -- beyond colorectal cancer," he added. "We think this screening could work for stomach, ovary, lung and the liver cancers, for which there aren't really any diagnostic tests for pre-symptomatic patients. And if one could detect even half of these pre-symptomatic patients, one could presumably spare those people a great deal of sickness and death, and that's hopefully what we're looking towards in the future."

Dr. Judith Collins -- the section chief for gastroenterology at the Veterans Affairs Medical Center and an associate professor of medicine at Oregon Health and Sciences University -- agreed that the future holds enormous promise for this type of cancer screening.

"This is the technology that we need and are hoping for, and I am confident that this is how we will diagnosis colon cancer in the future," she said.

"However, the downfall is that it tends to diagnose the tumors at a later stage," she noted. "So for now I think this would be a better diagnostic test for someone who's at very high risk for other diagnostic procedures, such as a colonoscopy. But while the clinical implication right now is perhaps less than the potential implication, I think the potential is huge."

SOURCES: Bert Vogelstein, M.D., Howard Hughes Medical Institute and The Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins Medical Institutions, Baltimore; Judith Collins, M.D., section chief, gastroenterology, Veterans Affairs Medical Center, and associate professor, medicine, Oregon Health and Sciences University, Portland; Oct. 24-28, 2005, Proceedings of the National Academy of Sciences online

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