The U.S. Food and Drug Administration (FDA) recently approved Guardant Health’s Shield blood test for colorectal cancer screening in adults 45 years and older who are at average risk for the disease. The first blood test to be approved by the FDA as a primary screening option for colorectal cancer, Shield can be ordered by health care providers similar to all other noninvasive methods recommended in the colorectal cancer screening guidelines.
AdventHealth oncologist Mohamedtaki Tejani, MD, and gastroenterologist Irteza Inayat, MD, recently sat down to discuss this new screening tool, including the benefits and limitations.
How Shield Works
The Shield test integrates genomics, epigenomics and proteomics to detect colorectal cancer signals in the bloodstream, including circulating tumor DNA (ctDNA), the DNA shed by tumors.
Dr. Tejani: In the field of oncology, we have already been using ctDNA to guide colorectal cancer treatment, enabling us to take a more effective and more personalized approach to managing each individual patient’s cancer. It helps us to reduce unnecessary treatment and detect changes earlier so that we can make prompt adjustments to treatment. We’ve found that ctDNA helps keep patients better informed and can improve their quality of life throughout their cancer care journey. When it comes to screening for colorectal cancer, colonoscopy remains the gold standard. However, adherence rates are much lower than we would like. The ctDNA technology within Shield provides another less invasive option that could improve compliance with screening guidelines, especially amongst younger patients.
Diagnosing Colorectal Cancer – The Challenges
Even though it is highly treatable if caught early, colorectal cancer is the second-leading cause of cancer-related death in the U.S. The American Cancer Society estimates that more than 150,000 people will be diagnosed with colorectal cancer in 2024 and that the disease will be responsible for more than 53,000 deaths.
Dr. Tejani: Despite the high cure rate when caught early, the colorectal cancer screening rate in the U.S. is only about 59%, falling well below the National Colorectal Cancer Roundtable’s goal of 80% for eligible individuals. In fact, more than one out of three eligible Americans—over 50 million people—do not complete colorectal cancer screening. In addition, we know that more than 75% of individuals who die from colorectal cancer are not up to date with their screening. Earlier detection is critical to saving lives. When colorectal cancer is found at an early stage before it has spread, the 5-year relative survival rate is 91%. However, if the cancer has metastasized, the 5-year survival rate is only 14%.
Dr. Inayat: The best screening test is the one that gets done. While colorectal cancer is the second leading cause of cancer-related death in the U.S., it is the number one cause in younger patients. Despite the increasing number of colon cancer cases in younger people in recent years and the new screening guidelines, a large percentage of those age 45-50 haven’t been screened. Shield provides us with another diagnostic tool that we hope will overcome some of the barriers and improve that. Many people believe that their options up until now, including colonoscopy or stool-based tests like FIT (fecal immunochemical test) and Cologuard (a multitargeted stool DNA test), are too invasive, unpleasant or inconvenient.
Effectiveness of the Guardant Shield Blood Test
Dr. Tejani: The approval of Shield was based on the results of the ECLIPSE study published in the March 2024 issue of The New England Journal of Medicine. It involved more than 20,000 average-risk adults and demonstrated 83% sensitivity for the detection of colorectal cancer, with 90% specificity for advanced neoplasia.
Dr. Inayat: This performance is within range of current guideline-recommended noninvasive screening methods, in which overall colorectal cancer sensitivity ranges from 74% to 92%. By comparison, colonoscopy has about a 99% overall sensitivity, the FIT-DNA test (Cologuard) is around 92%, and the FIT test comes in around 80%.
Limitations of the Shield Test
Dr. Inayat: The primary disadvantage of the Shield test is that it is not as good as colonoscopy and the other approved screening tests in detecting precancerous or early-stage cancers. The Shield test only had about a 13% sensitivity for detecting advanced polyps while colonoscopy has about 90% sensitivity and the FIT test around 24%.
As a gastroenterologist, my goal is to not only detect colon cancer, but to prevent it, and colonoscopy remains the only screening option that allows us to both identify and remove precancerous polyps. It is also important for patients to know that if the Shield test comes back positive, they will still need a diagnostic colonoscopy. Finally, as happens with new treatments, insurance often lags FDA approval so it may take some time for Shield to be covered by health plans. The current out-of-pocket cost runs around $895.
Dr. Tejani: Despite the limitations, the Shield test provides us another way to approach the problem. We are hopeful that having a blood test as an option will help improve screening adherence, detect more colorectal cancers earlier and ultimately, reduce colorectal cancer–related mortality. As effective as colonoscopy is as both a way of finding cancer and removing lesions that could become cancer later, we know many people are simply unwilling to undergo the procedure. That said, anyone considered high risk for colorectal cancer or cancer patients who are at secondary risk should only do colonoscopy.
