The U.S. Food and Drug Administration (FDA) has approved the Shield blood test, developed by Guardant Health, as the first blood-based screening tool for colorectal cancer (CRC) in individuals aged 45 and older who are at average risk. This landmark decision marks the integration of blood tests into the primary screening options for CRC, alongside traditional methods like colonoscopies and stool tests.
The Shield test, which detects colorectal cancer by identifying fragments of tumor DNA (ctDNA) in the bloodstream, was granted approval on Monday. It represents a significant advancement in CRC screening, offering a less invasive alternative for patients who might otherwise avoid more traditional and uncomfortable tests. According to Guardant Health, the test also qualifies for Medicare coverage. The company plans to disclose the test’s pricing within the week.
William Grady, MD, a gastroenterologist at Fred Hutchinson Cancer Center, praised the approval, noting that it enhances the accessibility of early detection tools for CRC, which is crucial for effective treatment. The FDA’s decision follows a favorable review by an advisory panel in May, which assessed evidence from a study led by Grady. This research, published in March in the New England Journal of Medicine, demonstrated that the Shield test successfully identified CRC in 83% of confirmed cases.
Despite its promising performance, the Shield test is not without limitations. It has a detection rate comparable to at-home stool tests but falls short of the accuracy provided by colonoscopies. Approximately 10% of participants received false positive results, where the test indicated CRC despite a clean colonoscopy.
FDA advisory panelist Vikesh Singh, MD, from Johns Hopkins Medicine, highlighted that while the Shield test offers a more convenient screening option, it may not provide the reassurance needed to forgo a colonoscopy if results are positive.
Colorectal cancer, the third most commonly diagnosed cancer in the U.S., can be effectively prevented through early detection. Researchers emphasize the importance of regular screening, as over a third of eligible individuals aged 45 to 75 are currently not up-to-date with their screenings.
The Shield blood test works by detecting ctDNA, which carries unique mutations indicative of cancer cells. This approach was tested on about 7,800 individuals without a history of CRC or related risk factors. The test achieved a sensitivity of 83% and a specificity of 90%, comparable to some stool-based tests like FIT and Cologuard.
While the Shield test adds an important option to the screening toolkit, experts agree that colonoscopy remains the gold standard due to its comprehensive visual examination of the colon and rectum. If the Shield test results are positive, a follow-up colonoscopy is still necessary to identify and remove precancerous lesions that the blood test may not detect.
The introduction of the Shield test is seen as a step forward in increasing screening participation rates, particularly among those who might avoid current methods. William Grady hopes that offering a blood-based option will encourage more people to engage in regular CRC screenings, addressing a critical gap in preventive care.
