The first big trial of a DNA test to detect colon cancer (search) proved disappointing to those hoping for an easy and accurate new screening method.

The test, which looks for signs of mutant genes in stool, found just half the colon and rectal cancers detected by colonoscopy. It did find four times as many cancers as a widely used test that looks for blood in stool, but the DNA test is too expensive — $400 to $800 — and too inaccurate to recommend, specialists said.

Earlier research had suggested that DNA tests might be a less expensive and more appealing option than colonoscopy, in which a long, flexible tube is inserted in the rectum.

The study in Thursday's New England Journal of Medicine (news - web sites) looked at 4,400 people who were at least 50 years old, had no symptoms of cancer and were at average risk of the disease. It was paid for by Exact Sciences of Marlborough, Mass., which makes the test.

The DNA test found 52 percent of the cancers found by colonoscopy, compared with 13 percent for the test that finds blood in stool, Dr. Thomas F. Imperiale of Indiana University reported.

The findings show that the genetic test cannot yet be recommended, Steven H. Woolf of Virginia Commonwealth University wrote in an editorial.

Earlier, small studies of the DNA test had success rates of up to 91 percent, and the blood test found 30 percent to 40 percent of cancers in earlier tests.

Only about half of Americans 50 and older have been screened for colon and rectal cancer, which are diagnosed in about 147,000 U.S. residents each year and kill almost 40 percent of them