FDA approves blood test for colon cancer detection
The Food and Drug Administration on Monday approved a new screening test for colorectal cancer. It requires only a sample of blood and can find cancers when they are early stage and usually curable.
For many people, a routine blood test is easier to get than a colonoscopy or a fecal sample test. But the blood test, made by Guardant Health of Palo Alto, California, comes with a limitation. Unlike other screening tests for colon and rectal cancers, it has a poor record of finding precancerous growths. Removal of those growths can prevent cancer.
The test, named Shield, will be available within a week. Guardant will announce its list price at that time, said Matt Burns, a company spokesperson. It is approved for people ages 45 and older who are at average risk for colon cancer.
The hope is that the blood test, despite its limitation, can encourage more people to be screened for colorectal cancer, the second-most common cause of cancer-related deaths in the United States. As many as 53,000 Americans are expected to die from colorectal cancer this year.
Regular screening can prevent as many as 73% of those deaths. But although current guidelines recommend screenings starting at age 45, as many as 25% to 50% of people who should be getting screened are not.
The problem is convincing more people to be screened. That is where the new test comes in. It is simple for patients — the blood sample can be obtained at a doctor’s office as part of a routine physical exam, or at a commercial lab.
The Shield test takes advantage of the fact that cancer cells and large polyps — clumps of cells on the lining of the colon that occasionally turn into cancers — shed fragments of DNA into the blood. By detecting those DNA fragments, the blood test can find cancers and some polyps.
In a study published March 13 in The New England Journal of Medicine, Guardant reported that its Shield test found 87% of cancers that were at an early and curable stage. The five-year survival rate for early stage cancers is 91% as compared with 14% if the cancer has spread outside the colon.
The false positive rate of the test was 10%. But it only found 13% of large polyps as compared with 95% with a colonoscopy.
On May 23, a committee that advises the FDA recommended that the blood test be approved. But the group cautioned that its inability to prevent cancer is a serious limitation and said they endorsed it because it may prompt people who forget or avoid colorectal cancer screening to be screened.
Current screening tests include fecal tests every three to five years or a colonoscopy every 10 years.
Some patients resist fecal tests that require them to mail samples of their feces to a lab to test for abnormal DNA and blood that can leak from cancers.
Others avoid colonoscopies because preparation for the procedure can require up to a day of fasting and taking a powerful laxative to cleanse the colon. Then, just before the colonoscopy, patients get anesthesia, which means they could lose a day of work and that someone must help them get home afterward.
But people who opt for a blood test may not escape having a colonoscopy: If the test indicates that the person might have colorectal cancer or a large polyp, they will need the procedure to find and remove the cancer or polyp.
Guardant said the test meets Medicare’s requirements for coverage. For those with Medicare part B there should be no additional cost, Burns said. The out-of-pocket cost for those with commercial insurance or Medicare Advantage will depend on the plan.
This article originally appeared in The New York Times.
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