FDA Panel Recommends Shield Blood Test for Colorectal Cancer Screening
A blood test designed to screen for colorectal cancer is one step closer to approval by the U.S. Food and Drug Administration (FDA). On Thursday night, the Medical Devices Advisory Committee, an FDA advisory panel, recommended the approval of the Shield blood test, finding it safe, effective, and beneficial despite potential risks.
Shield Blood Test Nears FDA Approval
Guardant Health, the company behind Shield, is seeking FDA premarket approval for the test to screen for colorectal cancer in individuals aged 45 and older at average risk. While Shield is not the first blood-based screening tool for colorectal cancer, it offers another option for detecting a type of cancer that increasingly affects younger Americans.
Shield is currently available commercially, but FDA approval would expand its availability and coverage, providing another screening choice. Guardant Health expects the FDA to decide on Shield’s premarket approval later in 2024. However, FDA approval is not guaranteed, as the agency sometimes diverges from its advisors’ recommendations.
Understanding Colorectal Cancer
Colorectal cancer starts in the colon or rectum and is often referred to as colon or rectal cancer, depending on its origin. According to the American Cancer Society (ACS), most colorectal cancers develop from polyps, growths on the inner lining of the colon or rectum. While most polyps are benign, some can become cancerous over many years.
Symptoms of colorectal cancer include changes in bowel habits, rectal bleeding, blood in the stool, abdominal pain, weakness, fatigue, and sudden weight loss. Despite an overall decline in cancer deaths, the ACS reported an alarming increase in colon cancer among younger adults earlier this year. Colon cancer is now the leading cause of death among men under 50 and the second leading cause of death among women in the same age group.
Traditional Colorectal Cancer Screening Methods
Colonoscopies remain the gold standard for screening colorectal cancer. During this procedure, a doctor inserts a colonoscope—a long, thin, flexible tube with a camera on the end—through the anus to examine the rectum and colon, potentially biopsying any suspicious tissues or polyps.
Stool tests can also detect blood not visible to the naked eye, possibly indicating cancer. The United States Preventative Services Task Force recommends that adults aged 45 and older with average risk undergo colorectal cancer screening. This includes a stool test every one to three years or a colonoscopy every 10 years for asymptomatic individuals.
How Shield Works
Shield detects colorectal cancer by identifying DNA shed by tumors in blood samples. Results are available about two weeks after the samples reach the laboratory. Clinical trial data published in The New England Journal of Medicine showed that Shield has an 83.1% sensitivity rate and an 89.9% specificity rate. This means 83.1% of patients with colorectal cancer detected by a colonoscopy tested positive on the Shield blood test, and 89.9% of patients without cancer tested negative.
During the FDA advisory panel meeting, eight out of nine advisers voted yes on safety, six out of nine voted yes on efficacy, and seven out of nine voted yes on benefits outweighing risks.
Guardant Health asserts that the blood test will eliminate barriers associated with current screening methods like colonoscopies or stool-based tests, which can be time-consuming or challenging to complete. The blood test can be performed without special preparation and as part of a standard doctor’s visit.
Potential Drawbacks
Despite the high overall sensitivity rate, clinical trial data indicated that the Shield test might miss one in ten people with precancerous lesions and one in 1,000 people with cancerous lesions. These “false negatives” could result in tests finding no evidence of cancer when patients actually have precancerous or cancerous lesions.
Data also showed that Shield missed about 87% of advanced precancerous lesions, with a specificity rate of just 13.2%. Shield did not detect small lesions of less than 10 millimeters.
While the majority of the panel voted in favor of the test, some FDA advisers expressed concerns about appropriate patient counseling, patient misunderstanding of a “negative test,” and the language used in packaging and labeling.
Conclusion
The FDA panel’s recommendation for the approval of the Shield blood test marks a significant step forward in colorectal cancer screening. While it is not without its drawbacks, the test offers an additional, less invasive option for individuals at average risk, potentially increasing screening rates and early detection. As Guardant Health awaits the FDA’s decision, the future of colorectal cancer screening could see a promising new addition.
