FDA Approves Blood Test to Screen for Colon Cancer

People living with colorectal cancer, their families, caregivers, and doctors were given a glimmer of hope on July 29, 2024, when the U.S. Food and Drug Administration (FDA) approved the Shield blood test for colon cancer screening. It is just the second blood test the FDA has approved for detecting the deadly cancer – anyone over 45 years old and over is eligible to use Shield.

Achieving Accessible and Accurate Diagnostics 

Colorectal cancer is the third most-common and second-deadliest type of cancer in the U.S. With Shield now approved to screen for the cancer, there is hope that more screenings can confirm the disease early in its development. CRI Keith Landesman Memorial Fellow Kevin Ng, PhD, with the Rockefeller University, said Shield’s FDA approval could have a significant impact on improving colorectal cancer immunotherapy research.  

“This new blood test is very exciting as it allows for patients to be diagnosed earlier,” Dr. Ng said. “Like many therapies, immunotherapy is most effective when treating early-stage tumors, and so increasing the rate of diagnosis could increase the proportion of patients that benefit from immunotherapy treatment.”

Another CRI-funded scientist, CRI-Torrey Coast Foundation GEMINI CLIP Investigator Valsamo Anagnostou, MD, PhD, is at the forefront of utilizing blood tests that screen circulating tumor DNA (ctDNA) to assess the risk of cancer recurrence and measure patient responses to immunotherapy in metastatic lung cancer and gastroesophageal patients. Dr. Anagnostou conducts her research at Johns Hopkins University School of Medicine.

With the approval of the Shield screening, patients can have their blood drawn as a diagnostic test option to screen for colorectal cancer. Shield can detect the DNA particles in the bloodstream emitted by cancer cells and large polyps, which are cell clusters on the colon that can become cancerous, thereby detecting the presence of cancer cells at a very early stage. 

Patients can easily get the blood test done either in a commercial lab or during a routine checkup with their physician. If the ease of getting tested with Shield can convince more people to get screened early, it could prove instrumental in increasing colorectal cancer survival rates. Only 40 percent of the cancer’s diagnoses are caught in the early stage, where the survival rate is 90 percent. There are currently eight FDA-approved immunotherapy treatments for colorectal cancer – four are monoclonal antibodies and four are checkpoint inhibitors. 

A Supplement – not an Alternative – to Colonoscopies 

While Shield is not a perfect alternative to colonoscopies, it is nonetheless effective. A scientific publication in March 2024 determined that the test is 83% accurate at detecting colorectal cancer in the blood. Currently, only between 25 and 50 percent of people who should be tested for colorectal cancer have it done.

The test’s FDA approval may be a bridge for some at-risk-people who are hesitant to go through the more involved colonoscopy process. CRI Lloyd J. Old STAR Ivan Zanoni, PhD, a research faculty member with Boston Children’s Hospital, agrees.

“I think this is the major strength of this new diagnostic tool. An individual that will test positive will have an even more important and pressing reason to undergo a colonoscopy,” Dr. Zanoni said.

Shield’s limitation is that it is not quite as accurate as colonoscopies at detecting colorectal cancer, and its accuracy with screening for precancerous growths is poor. Therefore, it is a supplement, not an alternative, to colonoscopies. It is a welcome tool for cancer patients and clinicians.