A screening method for colon cancer using a fecal DNA panel has been found to be more accurate than the standard fecal occult-blood test.
Colorectal cancer (cancer of the colon or rectum) is the second
leading cause of
death from cancer in the US. If caught early (in the polyp stage) it is treatable by surgery.
Checking the stool for
blood (fecal occult-blood testing) is currently the most widely used screening test for colorectal
cancer.
However, the test tends to miss a significant portion of cancers since many tumors do not actually
bleed. DNA
testing has a high degree of accuracy (sensitivity) in patients with symptomatic cancer, but it is not
known
whether DNA testing would be equally useful in patients with less advanced, non-symptomatic
lesions. A team
from the Colorectal Cancer Study Group has now compared the results of the standard Hemoccult
II (Beckman
Coulter) fecal occult-blood test with that of the DNA testing in 4404 asymptomatic patients over 50
years old and
at average risk for colorectal cancer. Results were compared to those obtained by colonoscopy, the
"gold
standard", in a random subgroup of 2507 patients.
Analysis showed that compared to the Hemoccult II test, the accuracy of the fecal DNA panel was four times greater for invasive cancer and more than two times greater for adenomas containing high-grade abnormalities (dysplasia). Of 31 invasive cancers, the fecal DNA panel detected 16 and the Hemoccult II detected 4 (51.6% vs. 12.9%); of 71 invasive cancers plus non-cancerous tumors (adenomas) with high-grade dysplasia, the fecal DNA panel detected 29 and the Hemoccult II detected 10 (40.8% vs. 14.1%); and, of 418 cases of uncontrolled cell growth (advanced neoplasia), the fecal DNA panel detected 76 compared to 45 detected by the Hemoccult II (18.2% vs. 10.8%). Furthermore, the level of accuracy with the fecal DNA panel was achieved with only a minor decrease in correct identification of subjects without disease who had no polyps on colonoscopy. The results suggest that the fecal DNA panel may be more accurate than the Hemoccult II test for the detection of early colorectal cancer, and the researchers note that the availability of a more accurate, non-invasive test might encourage more widespread screening.
Dr. Steven Woolf of Virginia Commonwealth University, in an accompanying editorial, points out
that fecal DNA
testing is vastly more expensive than fecal occult-blood testing ($400-800 per test compared to $3-
40 per test).
He also estimates that colorectal cancer will ultimately only be diagnosed in about 2% of people
(aged 50-59
years old) who have a positive fecal DNA test. NOTE: The research was supported by grants from
Exact
Sciences, the clinical laboratory used to determine results of the fecal DNA panel test for the
study. |
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