Guardant Health’s Shield blood test, currently available only with a doctor’s prescription, represents a significant step forward in cancer detection. By offering a more accessible and less invasive screening option, experts are optimistic that it will encourage a higher number of individuals to undergo screening, potentially catching cancer at an earlier, more treatable stage.
A noteworthy aspect of the Shield test is its ability to detect colorectal cancer with considerable accuracy. Clinical trials have shown that the test can identify colorectal cancer approximately 83 percent of the time. This level of precision is promising, as early detection is crucial in improving survival rates for this type of cancer. However, the test’s ability to detect precancerous lesions, which are often precursors to full-blown cancer, is more limited, with an accuracy of about 13 percent.
Currently, the Shield test is available by prescription for a price of $895. While this might seem steep, it is important to consider that FDA approval, which is still pending, could pave the way for broader insurance and Medicare coverage. Such approval would not only make the test more affordable but also more widely accessible, potentially increasing its use and impact in the early detection of colorectal cancer.
A Revolutionary Step in Colorectal Cancer Detection: The Shield Blood Test
A new blood test has emerged as a significant advancement in the detection of colorectal cancer, boasting an accuracy rate that could rival existing screening methods. According to a study published on March 14, 2024, in The New England Journal of Medicine, the Shield blood test can accurately identify 5 out of 6 cases of colorectal cancer. This new test offers a more streamlined and less invasive alternative to the current colorectal cancer screening options, potentially increasing patient compliance and early detection rates.
The Promising Results and Expert Insights
William M. Grady, MD, a gastroenterologist at the Fred Hutch Cancer Center in Seattle and the study’s corresponding author, highlighted the potential impact of the Shield test. “That accuracy rate is close to at-home stool tests used for early detection of colorectal cancer,” Dr. Grady noted, emphasizing that this blood-based test could serve as a crucial alternative for patients who might be hesitant about the more invasive screening methods currently available.
On May 23, 2024, an advisory panel for the U.S. Food and Drug Administration (FDA) voted in favor of approving the Shield blood test. The panel’s vote was overwhelmingly positive: 8-1 in favor of the test’s safety, 6-3 in support of its effectiveness, and 7-2 endorsing its benefit-risk profile. Given the FDA’s tendency to follow its advisory committees’ recommendations, official approval of the Shield test seems imminent, which would likely pave the way for insurance and Medicare coverage, making it more accessible to a broader population.
The Significance of a New Screening Method
The introduction of an additional screening option for colorectal cancer is a welcome development in the medical community. Sean Langenfeld, MD, a colorectal surgeon at Nebraska Medicine in Omaha, who was not involved in the study, commented on the importance of this advancement. “Colorectal cancer is common, deadly, and preventable. It’s the third most common cancer and the second leading cause of cancer-related death,” he stated. Despite these alarming statistics, Dr. Langenfeld pointed out that only about 60 percent of the population undergoes appropriate screening.
The FDA advisory committee also acknowledged some limitations of the Shield blood test. “It’s a good colon cancer screening test, but for later-stage colon cancer,” remarked Dr. Karla Ballman, PhD, of the Mayo Clinic College of Medicine and Science in Rochester, Minnesota, in an interview with MedPage Today. She further noted that the test is less effective in detecting stage 1 colorectal cancer and advanced adenomas, which are precancerous lesions.
Since its launch in May 2022, the Shield test has been utilized by over 20,000 people, though it remains accessible only by prescription. The cost of the test is $895, which most users likely pay out of pocket, underscoring the need for insurance coverage to broaden its reach.
Early Detection: A Lifesaving Measure
The landscape of colorectal cancer incidence has evolved over the past few decades. While the overall rate of colorectal cancer has decreased, there has been a concerning rise in cases among younger adults. The number of individuals under 55 diagnosed with colorectal cancer has nearly doubled in the last 30 years, highlighting the need for effective and accessible screening methods.
Early detection remains critical in improving survival rates. When colorectal cancer is diagnosed at an early stage, before it has spread, the five-year relative survival rate is an encouraging 91 percent. However, once the cancer has metastasized to distant parts of the body, the survival rate plummets to just 13 percent. The availability of a blood-based screening test like Shield could encourage more people to undergo screening, as it is perceived as less invasive, potentially increasing screening rates and saving lives.
Comparing Shield with the ‘Gold Standard’ Colonoscopy
To evaluate the accuracy of the Shield blood test against the current gold standard for colorectal cancer screening—a colonoscopy—researchers conducted a study involving nearly 8,000 participants aged between 45 and 84. The average age of participants was 60 years, with a demographic distribution that reflected the 2020 U.S. Census: 78.5 percent were white, 12 percent were Black, and 7 percent were Asian. About 13 percent identified as Hispanic or Latino.
Participants were required to have an “average risk” for colorectal cancer, meaning no family history of the disease, no personal history of cancer, and no diagnosis of inflammatory bowel disease or large polyps. Of the 7,861 individuals who met these criteria and completed both a colonoscopy and the Shield blood test, 65 were found to have colorectal cancer through the colonoscopy. Of these, 54 cases were also detected by the Shield blood test, translating to an accuracy rate of approximately 83 percent.
The Shield test demonstrated higher sensitivity in identifying colorectal cancers, including early-stage cancers, but was less effective in detecting advanced precancerous lesions. This suggests that while the Shield test is a powerful tool for cancer detection, it may not replace colonoscopy, particularly for identifying precancerous conditions that could eventually develop into cancer.
How Does the Shield Test Compare to Other Screening Options?
While a colonoscopy remains the most reliable method for detecting polyps and colorectal cancer, it is also the most invasive. The procedure requires several preparatory steps, including a special diet, bowel cleansing with laxatives, and sedation or anesthesia. If no abnormalities are found, the test only needs to be repeated every 10 years. However, the invasiveness and preparatory demands of a colonoscopy can deter some individuals from undergoing the procedure.
In addition to the Shield blood test, there are two main at-home tests for colorectal cancer screening currently available:
- Fecal Immunochemical Test (FIT): This test has an accuracy rate of about 79 percent for detecting colorectal cancer. The test involves collecting a small fecal sample at home and sending it to a lab for analysis. The test is recommended every one to two years.
- Cologuard (Fecal DNA Testing): Cologuard offers a higher accuracy rate of 92 percent. Like the FIT test, it involves collecting a fecal sample and mailing it to a lab. The test is recommended every three years.
Dr. Langenfeld notes that the Shield blood test’s accuracy in detecting colorectal cancer is comparable to that of the FIT test but slightly lower than Cologuard’s sensitivity. However, the Shield test boasts a specificity of 90 percent, meaning it has a low rate of false positives. The Shield test also needs to be repeated every three years, and a positive result would necessitate a follow-up colonoscopy to confirm the presence of cancer.
Who Should Consider the Shield Colorectal Cancer Test?
The Shield test is particularly suited for patients who are unable or unwilling to undergo a colonoscopy. Dr. Langenfeld explains, “This test is most appropriate for patients unable or unwilling to undergo colonoscopy — that’s who I would recommend it to. Since it is fast, easy, and noninvasive, it will seem like less of a commitment, and will hopefully lead to people undergoing screening who would have otherwise continued to put it off for the foreseeable future.”
However, it is important to recognize that the Shield test was less effective in identifying precancerous lesions, detecting only 13 percent of them. “I will still recommend screening colonoscopy for most patients,” Dr. Langenfeld adds, emphasizing the importance of the colonoscopy’s ability to not only detect but also remove precancerous polyps during the procedure.
Polyps are common, especially in older adults, and while most are benign, some can become cancerous over time. The ability to remove these polyps during a colonoscopy is a significant preventive measure that blood tests like Shield cannot offer.
Dr. Grady advises patients to discuss their options with their healthcare providers to determine the best screening method for their individual needs. Currently, when given the choice between stool-based tests and colonoscopy, nearly half of patients opt for neither, which underscores the need for a test like Shield that may be perceived as less invasive and more acceptable to patients.
When Should You Begin Colorectal Cancer Screening?
Both the American Cancer Society and the U.S. Preventive Services Task Force recommend that individuals at average risk begin colorectal cancer screening at age 45. For those with health insurance, these screenings may be covered with little to no out-of-pocket cost. More information about colorectal cancer screening options can be found on the Centers for Disease Control and Prevention’s website.
Final Thoughts
The Shield blood test represents a promising advancement in colorectal cancer screening. With the potential for FDA approval on the horizon, this test could become a vital tool in increasing screening rates and early detection, ultimately saving lives. While it may not replace colonoscopy, especially for detecting precancerous lesions, it offers a less invasive option that could appeal to those who might otherwise forgo screening altogether.
As with any medical decision, it is crucial for patients to consult with their healthcare providers to choose the most appropriate screening method based on their personal health history and risk factors.
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