Gene-Based Blood Test Might Help Spot Colon Cancer
Early study found it had high accuracy, but experts say it won't replace colonoscopy anytime soon
Friday, June 7, 2013
The test accurately spotted 87 percent of colon cancers across all cancer stages, and also correctly identified 95 percent of patients who were cancer-free, the researchers said.
Colon cancer remains the second leading cancer killer in the United States, after lung cancer. According to the U.S. Centers for Disease Control and Prevention, nearly 137,000 Americans were diagnosed with the disease in 2009; 40 percent of people diagnosed will die from the disease.
Right now, invasive colonoscopy remains the "gold standard" for spotting cancer early, although fecal occult blood testing (using stool samples) also is used. What's needed is a highly accurate but noninvasive testing method, experts say.
The new blood test looks at the "methylation" of genes, a biochemical process that is key to how genes are expressed and function. Investigators from Genomictree Inc. and Yonsei University College of Medicine in Seoul said they spotted a set of genes with patterns of methylation that seems to be specific to tissues from colon cancer tumors. Changes in one gene in particular, called SDC2, seemed especially tied to colon cancer growth and spread.
As reported in the July issue of the Journal of Molecular Diagnostics, the team tested the gene-based screen in tissues taken from 133 colon cancer patients. As expected, tissues taken from colon cancer tumors in these patients showed the characteristic gene changes, while samples taken from adjacent healthy tissues did not.
More important, the same genetic hallmarks of colon cancer (or their absence) "could be measured in [blood] samples from colorectal cancer patients and healthy individuals," the researchers said in a journal news release.
The test was able to detect stage 1 cancer 92 percent of the time, "indicating that SDC2 is suitable for early detection of [colorectal cancer] where therapeutic interventions have the greatest likelihood of curing the patient from the disease," study lead author TaeJeong Oh said in the news release.
Oh said the test could be used either in addition to conventional colonoscopy or perhaps as an alternative.
Experts were cautious about the potential utility of the new test.
"Given the overall low rate of adherence to colorectal cancer screening, having other non-invasive options to get everyone screened for colorectal cancer is never a bad thing," said Dr. Bethany Devito, a gastroenterologist at North Shore University Hospital in Manhasset, N.Y.
Devito said, however, that more research is needed before the blood test becomes fully accepted for use. Unlike similar gene-based tests based on stool samples, the new test "has not been studied to prove detection of precancerous polyps," she said. "Further studies with larger sample sizes are needed to validate its role as an effective screening tool for the detection of not only early colorectal cancer but also precancerous polyps."
Dr. Richard Fogler, chairman emeritus of the department of surgery at Brookdale University Hospital and Medical Center in New York City, said it's far too early to say that such a blood test could eliminate the need for colonoscopy.
Even if the accuracy of the SDC2 test is confirmed in further study, "all potential positive results will still require colonoscopy for definitive treatment planning," he said. "Since digital rectal exam and test for occult blood [in stool] continues to stand the test of time for convenient, painless and inexpensive screening, one would believe that it won't yet be replaced by SDC2, especially depending on the cost of the test compared with how much diagnostic value it adds."
Devito said the test might end up having a role in guiding treatment. "Because SDC2 methylation in [blood] is frequently detected across all colorectal cancer stages, this approach may be useful for monitoring colorectal cancer recurrence in patients that have already undergone treatments for their cancer," she said.