Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection. Credit | iStock
Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection. Credit | iStock

Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection 

United States: To assess for colon and rectal cancers, the majority of individuals undergo colonoscopies, which may feel intrusive and necessitate anesthesia, or they may opt for an at-home stool test, which can be more convenient but also awkward — and not appealing for those who are easily unsettled. 

However, a straightforward blood examination could soon become more widely accessible. 

The Shield is a blood test by Guardant Health, a biotech firm based in Palo Alto, California with the purpose of screening the early stages of colorectal cancer Guardian Health a bioteck firm situated in the Palo Alto, California state in the US has submitted Shield, a blood test for approval by the Food and Drug Administration abbreviated FDA. More recently, an FDA expert panel met to consider the data back on this screening test. 

The FDA Molecular and Clinical Genetics Panel of the Medical Devices Advisory Committee sat down to deliberate on the advantages and possibly the disadvantages of the test, and voted after on whether the test was safe and efficient or not as CNN Health reported.  

It reached 8-1 for the safety of the Shield test for anyone who now meets the testing criteria, 6-3 on the efficiency in regard to the criteria, and 7-2 on the benefits versus risk in relation to the testing. 

The deliberations and voting outcomes will be conveyed to the FDA, which considers but is not bound by the committee’s recommendations in its decision-making process regarding test approval. 

Should Shield secure FDA approval, it would mark the first sanctioned blood screening test for colorectal cancer meeting Medicare reimbursement requirements, noted Dr. Craig Eagle, chief medical officer at Guardant Health. 

Existing colorectal cancer screening options for individuals at average risk include stool-based tests performed annually or triennially; traditional colonoscopies performed every decade; virtual colonoscopies conducted every five years; or sigmoidoscopies, which entail using an endoscope to examine the lower colon, performed every five years. 

Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection. Credit | iStock
Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection. Credit | iStock

The Shield blood test is currently available as a laboratory-developed test (LDT), thus not necessarily necessitating FDA approval for performance under current regulations. However, FDA approval could enhance the test’s accessibility and coverage as an additional primary screening option. 

The test would not supplant commonly used screening methods but rather offer an additional non-invasive option, potentially increasing screening compliance, according to Guardant. 

“Present primary non-invasive screening options are confined to stool-based tests,” Eagle expressed in an email. “Our Shield blood test provides patients with a convenient alternative that demonstrates a validated level of performance comparable to non-invasive tests.” 

Various research groups and companies have been striving to devise simple blood tests for colorectal cancer screening. 

“The contention is that a point-of-care blood test can substantially reduce the incidence of advanced disease and save lives, even if it has less potential to avert the disease,” remarked Robert Smith, senior vice president of Early Cancer Detection Science at the American Cancer Society. 

A blood-based test would be unable to identify suspicious lesions or polyps in the colon or rectum, unlike a colonoscopy. With visual examinations such as colonoscopies or sigmoidoscopies, lesions or polyps with cancer development potential can be identified and excised, thereby preventing the disease, as reported by CNN.  

“Most individuals would welcome a blood-based option that exhibited greater accuracy in detecting precursor lesions alongside cancers. However, what is remarkable about colorectal cancer screening is the variability in individuals’ readiness to undergo one test over another,” Smith elucidated. “Choice must be offered to individuals.” 

Guardant’s Shield test is intended for colorectal cancer screening in individuals aged 45 or older with average disease risk, according to FDA meeting materials. The US Preventive Services Task Force advocates for colorectal cancer screening initiation at age 45 for average-risk individuals

The test is not recommended for high-risk individuals, such as those with personal or family histories of the disease. Individuals receiving an “abnormal” Shield test result would be referred for a colonoscopy. 

Since the debut of the lab-developed Shield test in May 2022, it has been utilized by over 20,000 individuals, with over 90% of those prescribed the test completing it, as per Guardant Health. 

“Every test developer understands that FDA approval is essential for significant adoption of their test,” Smith acknowledged. 

Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection. Credit | Canva
Breakthrough Blood Test Offers New Hope in Colorectal Cancer Detection. Credit | Canva

Mixed perspectives on efficacy 

During the recent meeting, FDA advisers displayed varying opinions regarding the test while responding to three questions concerning its safety, effectiveness, and risk-benefit balance. 

“I voted affirmatively on all three counts, with the understanding that this is intended for asymptomatic individuals for colon cancer detection. I believe it fulfills that purpose,” stated panelist Dr. Sean Spencer, a gastroenterologist and physician-scientist at Stanford University. 

“I think the labeling should explicitly state that this is not intended for adenoma detection and is not devised as a preventative measure,” Spencer suggested. Adenomas refer to non-cancerous tumors. 

Panelist Dr. Charity Morgan also voted affirmatively across all categories. 

“My rationale closely mirrored Dr. Spencer’s: the intention is for colorectal cancer detection. Had the intention included advanced adenomas, my vote might have been different,” Morgan, a professor at the University of Alabama at Birmingham, remarked. 

“I harbored reservations about efficacy due to the limited sensitivity for stage I. If the labeling clearly indicated that this test is robust in detecting stages II, III, and IV, my tentative yes would become a resounding yes,” she added. “Nevertheless, I concluded that they demonstrated efficacy as well as safety and a favorable risk-benefit profile.” 

Conversely, panelist Dr. Padma Rajagopal opined that while the test is deemed safe and the benefits outweigh the risks, she questions its efficacy due to limitations in detecting advanced adenomas and its inferior performance in identifying stage I cancers compared to advanced disease. 

“Should there be refinements in the indicated use or in the manner in which providers and patients are educated, I would reconsider my stance,” conveyed Rajagopal, a physician-scientist at the National Cancer Institute, the reports by CNN outlined.  

Panelist Dr. William Brugge expressed his view that while he considers the Shield test safe, he doubts its efficacy or that the benefits outweigh the risks. 

“My primary concern is that I don’t regard Shield as a particularly effective colon cancer screening test,” remarked Brugge, a gastroenterologist at Mount Auburn Hospital in Cambridge, Massachusetts. He asserted that he believes “many of the other existing tests” outperform it. 

The FDA advisers’ decisions will not immediately influence or alter the American Cancer Society’s screening recommendations, Smith clarified. 

“The American Cancer Society typically awaits FDA approval at this level before incorporating a test into our guidelines,” Smith noted. 

“We eagerly anticipate the FDA’s perspective on this test, and in terms of guidelines, I cannot predict the actions of any specific organization, including ours, as it entails a process involving extensive literature and evidence review, as well as consideration of the FDA decision and its implications,” he added. “It’s a deliberative process.” 

The operational mechanism of the test 

The Shield test functions by identifying tumor DNA in blood samples, necessitating a physician’s order for the test and kit for their patient. 

A study published in March in the New England Journal of Medicine found the test to exhibit approximately 83% sensitivity and 90% specificity. Sensitivity denotes a test’s accuracy in identifying individuals with the disease, categorizing them as positive. Specificity refers to its precision in designating individuals without the disease as negative.