Blood Test Added to Updated Colorectal Cancer Screening Guidelines
Key Takeaways:
- The U.S. Food and Drug Administration-approved Shield blood test is now included in the updated American Cancer Society colorectal cancer screening guidelines
- The Shield test is a non-invasive screening option for colorectal cancer that detects circulating tumor DNA through a simple blood draw
- The Shield test detected colorectal cancer in 83% of patients in a clinical trial, but abnormal results must be confirmed with a colonoscopy
Another tool available in the fight against colorectal cancer has been added to the American Cancer Society’s guidelines for colorectal cancer screenings. The blood-based screening test called Shield is a new option available to those 45 and older at average risk of developing colorectal cancer.
The test received approval from the U.S. Food and Drug Administration in 2024. It isn't intended to replace traditional screening colonoscopies, but there is hope that this non-invasive test will lead more people to seek out potentially life-saving screenings.
How It Works
The Shield test is performed using a simple blood draw. Once the sample is collected, it’s examined to find cancer cells left behind in the bloodstream called circulating tumor DNA. Patients with an abnormal test result should be referred for a colonoscopy.
Results of a clinical trial published earlier this year in The New England Journal of Medicine show that a blood-based screening test detected colorectal cancer in 83% of people with the disease.
While the test is an exciting new option, doctors say a screening colonoscopy is still the best option when it comes to detecting and preventing disease.
“We know that most colon cancers develop from pre-cancerous polyps. It is by removal of these polyps that we prevent colon cancer,” said Mark Friedman, MD, a gastroenterologist in Moffitt Cancer Center’s Gastrointestinal Oncology Department. “This can only be done with a colonoscopy and that is why it remains the gold standard screening test. Stool and blood-based tests do not detect polyps well and only detect cancer once it has developed.”
In 2022, the U.S. Preventive Services Task Force recommended that people of average risk start colorectal cancer screenings at age 45. This includes people with no prior diagnosis of colorectal cancer, no family history or genetic disorders that increase your risk of disease, no history of precancerous polyps and no diagnosis of inflammatory bowel disease.
More than 1 in 3 eligible adults are not screened as recommended, according to the American Cancer Society.
While a blood test may be less invasive than a colonoscopy, it can detect cancer only when it’s already developed. During a colonoscopy doctors can find and remove polyps five to 10 years before they potentially turn into cancer.
Other Options
Tiago Biachi, MD
In addition to colonoscopy, other recommended screenings include computed tomography colonography and stool-based tests with high sensitivity such as fecal immunochemical tests (FIT) that are widely accessible and would require a colonoscopy follow-up if the test comes back abnormal.
Results of a study of patients in California found a 33% reduced risk of dying of colorectal cancer for those taking at least one FIT screening. The findings were published recently in JAMA Network Open.
A positive blood or FIT test isn’t an official diagnosis, so anyone who tests positive would need a colonoscopy to confirm if there is disease. In addition, only a colonoscopy can tell doctors where tumors are hiding in the colon.
“The location of colorectal tumors can determine whether patients need surgery or chemotherapy and radiation before surgery,” Tiago Biachi, MD, PhD, a gastrointestinal oncologist at Moffitt said. “This blood test is not a home run for cancer diagnosis.”
The Shield test is given every three years starting at age 45. People with symptoms of colon cancer or a family history of the disease should still speak with their doctor about a colonoscopy.
