Jan. 24, 2008 (Orlando) -- A novel blood test holds promise for both detecting and preventing colon cancer, researchers report.
The test spots a protein called colon cancer-specific antigen-2 (CCSA-2) that is elevated in the presence of colon cancer or growths that are destined to become colon cancer. In contrast, the protein appears to be rare in low-risk colon polyps and healthy tissue.
"Right now, we really don't have a simple, accurate, and noninvasive method for detecting colon cancer. CCSA-2 is a blood protein that predicts the presence of the cancer with a low false-positive and false-negative rate," says Nicholas J. Petrelli, MD, of the Helen F. Graham Cancer Center in Wilmington, Del.
"Just as importantly," Petrelli tells WebMD, the test detects "high-risk premalignant polyps which, if left alone, will directly lead to cancer. If we remove them, we can prevent colon cancer from developing."
Petrelli moderated a news briefing to discuss the findings, which are being presented at the annual Gastrointestinal Cancers Symposium (GCS) this weekend in Orlando.
CCSA-2 Test Unique
Colorectal cancer is one of the most common forms of cancer, diagnosed in more than 150,000 people each year in the United States. Although colonoscopy can detect the disease at an early stage when it is most curable -- and even prevent it by finding polyps before they become cancerous -- many people avoid the procedure because of discomfort, pain, and a small risk of complications.
There are other noninvasive tests for colorectal cancer, such as the fecal occult blood test, which looks for blood in the stool. But occult, or hidden, blood is also found in the stool of people with a host of other conditions, such as hemorrhoids, resulting in false-positive results in up to 90% of cases.
The same research team reported earlier last year that two of CCSA-2's cousins, known as CCSA-3 and CCSA-4, can also indicate the presence of colorectal cancer.
The CCSA-2 test is unique in that it can distinguish between people who have advanced, high-risk adenomas (growths almost certain to become colon cancers) and non-advanced, low-risk adenomas or polyps that almost certainly will not lead to cancer, says researcher Eddy S. Leman, PhD, an instructor in the department of urology at Johns Hopkins Hospital in Baltimore.
"The higher the level of CCSA-2 in the blood, the greater the chance of having colorectal cancer or a high-risk adenoma," he tells WebMD.
Missed 9% of Cancers
In preliminary studies, the researchers tried the test on 135 people who had undergone colonoscopies: 28 had colon cancer, 18 had advanced adenomas, 59 had non-advanced adenomas or polyps, and 30 showed no sign of colon cancer. Blood samples from 125 more people with disorders other than colon cancer were also analyzed.
Results showed that the test had an overall sensitivity of 91%, meaning that only 9% of colon cancers or advanced adenomas were missed.
The specificity was 80%, meaning that the test gave false-positive results to 20% of people who didn't have the cancer or advanced adenomas. The research was funded by Onconome Inc., which holds the license for the technology.
The next step is to validate the findings in studies of larger groups of people, Leman says.
Results Early, but Exciting
Petrelli, a spokesman for the conference, says, "In view of the fact that we don't have a blood test to determine if a patient has colon cancer or premalignant polyps, the specificity and sensitivity rates are not bad in the research setting."
If the results can be reproduced, Petrelli says he foresees that people with positive test results would be sent on to colonoscopy to confirm the diagnosis. What about people with negative results? At this point, the need for a colonoscopy can't be ruled out, Petrelli says.
Leman agrees, but says that in the future the researchers hope to develop a blood test with 100% sensitivity and specificity, perhaps by testing for CCSA-2, CCSA-3 and CCSA-4 simultaneously. "Then, if you had [a low level of these blood markers], you might not need a colonoscopy," he says.
"The results are exciting, but there is so much more research that still has to be done," Petrelli says.