Johns Hopkins researchers are developing a simple blood test that can help doctors determine who needs a colonoscopy, a screening procedure for colon cancer recommended for all adults over 50 - but one considered so unpleasant that many avoid it.
The new test, which looks for cancer-related proteins in the blood, identifies colon cancer and precancerous polyps almost as well as a colonoscopy, according to a study published in the journal Cancer Research.
The authors say their test won't replace colonoscopies but might provide a noninvasive means of identifying high-risk patients - and an incentive for them to undergo the more invasive procedure.
"Part of what we are trying to do here is use blood markers for cancer like we do cholesterol levels to predict heart disease risk," said Robert H. Getzenberg, a cancer researcher at the Johns Hopkins School of Medicine and lead author of the paper. "If I could tell you you have a 92 percent chance of having colon cancer, you might be more willing to undergo a colonoscopy."
The blood test might also reduce the overall number of people who need a colonoscopy by screening out low-risk patients. "Someone at high risk should have the test right away, while someone who tests negative may not need to be looked at for another year," Getzenberg said.
As the United States' population ages and more people require screening, he added, the number of patients is likely to outpace the number of doctors available to perform colonoscopies. A preliminary blood screening could reduce some of the demand, experts said - if the test proves valid in larger studies and receives federal approval.
This year in the U.S., about 150,000 people will be diagnosed with colorectal cancer and 52,000 people will die from the disease, according to the National Cancer Institute.
Doctors use several tools to screen for colon cancer and precancerous lesions, including blood tests and imaging technologies such as X-rays and CT scans (also known as "virtual" colonoscopies). Another promising new test identifies genetic markers for cancer in stool samples.
A traditional colonoscopy, however, is considered the most accurate test. The American Cancer Society recommends that patients undergo at least one colonoscopy every 10 years, beginning at age 50. African-Americans and those with a family history of colorectal cancer should begin screening earlier, experts say.
The problem: The procedure requires fasting, consumption of powerful laxatives, anaesthesia and the insertion of a optical scope in the rectum. It also carries the risk of a punctured colon.
This combination has given colonoscopy its unpleasant reputation, and that might explain why fewer than half of all Americans who should have a colonoscopy get one, said Dr. Lisa S. Pichney, a gastroenterologist affiliated with St. Joseph Medical Center in Towson.
Hopkins' Getzenberg decided to look for a new screening method when he was working at the University of Pittsburgh and a colleague bemoaned the lack of a noninvasive, early test for colon cancer.
Getzenberg focused his search on blood-borne indicators related to structural abnormalities in cancerous cells.
"In cancer cells, the nucleus looks sort of angry, it's out of shape," he said. "We looked for a marker that was related to those structural changes in the nucleus."
Researchers isolated two proteins, known as CCSA-3 and CCSA-4, that appear to be released into the bloodstream when some of the cancer cells in a tumor die off.
In the study published last week, the researchers tested 107 patients for the proteins and used the results to determine if they had cancer or were at risk for cancer.
The patients then underwent colonoscopies, and the results from the two tests were compared.
The blood test found that 28 of the patients had cancer, the same number of cases discovered by colonoscopy. The test was slightly less apt at finding precancerous polyps - it found 14 of the 18 cases that were discovered by colonoscopy.
Pichney noted that the initial study was a small one, and that more extensive research is needed. But if the test proves accurate in larger studies, she said, it could result in more high-risk patients getting appropriate screening.
"I don't think this will replace standard colonoscopy, but if the test works out, it would be great," she said. "You do save lives if you pick up polyps early enough."
Dr. Jean-Pierre Raufman, head of gastroenterology at the University of Maryland School of Medicine, said screening for colon cancer might begin earlier in life if the blood test proves safe and effective.
"We chose 50 as the starting age with the notion that colonoscopy is an expensive test that carries some risk," he said. "If you could do the same thing with a blood test or a stool test, that would be a great thing. Maybe people would be tested in their 40s."
Getzenberg and colleagues are seeking FDA approval for the blood test and have just begun a clinical trial with a larger number of patients. They expect to complete the study within two years.
Colorectal cancer snapshot
This year in the United States, more than 150,000 people will be diagnosed with colon cancer, and more than 52,000 people will die from the disease.
Annually, $8.4 billion is spent in treating the disease.
Colorectal cancer is the fourth-most-common cancer among men and women, but men are more vulnerable after age 50.
More than 90 percent of cases are diagnosed after age 50, and the average age of diagnosis is 72.
[Source: National Cancer Institute]