By Brooke Mallory, OAN Staff
Monday, July 29, 2024 12:37 PM
On Monday morning, the US Food and Drug Administration (FDA) approved a blood test to screen for colon cancer in people considered to be at “average risk.”
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The blood test, called SHIELD, is manufactured by Guardant Health, and while the test is currently available on the market, FDA approval will help improve insurance coverage and availability.
If you are at “average risk” for colon cancer and are age 45 or older, the test is FDA approved.
“What does average risk mean? For screening purposes, you are at average risk of colorectal cancer if you do not meet the following criteria:
- A personal history of colorectal cancer or certain types of polyps.
- Family history of colon cancer;
- Confirmed or suspected hereditary colorectal cancer syndromes, such as familial adenomatous polyposis (FAP) or Lynch syndrome (hereditary nonpolyposis colorectal cancer or HNPCC).
- a history of inflammatory bowel disease (ulcerative colitis or Crohn’s disease), or
- According to the American Cancer Society, you have a “history of radiation therapy to the abdomen or pelvis for a previous cancer.”
Experts caution that while the blood test is not a complete substitute for a colonoscopy, it may encourage more people to get it because it takes less time and effort, and because colonoscopies are more accurate at detecting cancer, they are recommended every 10 years, as opposed to the three-yearly blood test.
“The Shield test has a false positive rate of about 10 percent, and while colonoscopies in clinical trials found 95 percent of large polyps, the Shield test found only 13 percent.” ABC News report.
SHIELD uses DNA from blood samples shed by lesions to identify colon cancer, and it takes about two weeks for results to be available after the laboratory receives the sample.
Still, colonoscopy is still considered the gold standard for colorectal cancer screening, and Shield is not the first blood-based screening method.
The Medical Device Advisory Committee (MDAC), an advisory group to the FDA, recommended earlier this year that the test be approved by the federal health agency. FDA approval is not always granted, but the agency typically agrees with its advisers.
SHIELD was reported to have a sensitivity of 83.1% in clinical trial data published in 2009. New England Journal of MedicineThis means that 83.1% of people whose colon cancer was found during a colonoscopy had a positive SHIELD blood test, and the specificity was 89.9%, meaning that 89.9% of people without cancer had a negative blood test result.
The data shows that despite high overall sensitivity, Shield may miss 1 in 1,000 malignant lesions and 1 in 10 precancerous lesions.
Clinical data suggests that these “false negative” results may lead to tests that miss malignant lesions when in fact patients have precancerous or cancerous lesions.
Despite concerns from MDAC members about false-negative results, the committee concluded that the test is safe and effective, and that the benefits of its use outweigh the drawbacks.
“The FDA approval of the SHIELD test is a huge win for patients and a key milestone in Guardant Health’s mission to defeat cancer with data. SHIELD will help increase colon cancer screening rates, allowing us to detect more cancers at an earlier, treatable stage,” said Amir-Ali Tarazaz, co-CEO of Guardant Health.
“We are currently preparing to launch this test in the near future and are excited to offer a viable blood-based testing option that allows physicians to tailor their testing regimens to their patients’ unique needs,” he added.
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