New Blood Test Can Detect 83% of Colon Cancers

If approved by the U.S. Food and Drug Administration, the new test could be a more attractive alternative to stool tests or colonoscopy.

In the United States, around one out of three adults 45 years or older are not getting the recommended screenings for colorectal cancer. Moreover, the number of colon cancer cases among younger people is growing, but scientists aren't sure why.

The U.S. Preventive Services Task Force recommends that adults aged 45 to 75 should be screened for colorectal cancer. They also say that people ages 76 to 85 should talk with their healthcare provider when deciding whether to get screened.


Colonoscopy is the gold standard for colorectal cancer screening. However, typically, people who choose this screening method must take strong laxatives before the procedure to ensure the bowels are clear. This pre-colonoscopy protocol, combined with having to undergo a slightly invasive procedure under anesthesia, can cause some people to avoid getting the screening they need.

An alternative screening tool called Cologuard® (FIT-DNA) may be a more acceptable option for some people. However, this test involves collecting a stool sample at home and sending it to a lab for analysis, which can be off-putting for some individuals.

Computed tomographic colonography (CTC) scans, flexible sigmoidoscopy, and stool tests such as the fecal immunochemical test (FIT) and high-sensitivity guaiac-based fecal occult blood test (gFOBT) are other screening options. Still, they may not be as effective at detecting colon cancer as FIT-DNA tests or colonoscopy.

Now, a new, more convenient colon cancer test may be available soon for people who are hesitant about getting screened.

In a study published on March 14 in The New England Journal of Medicine, researchers found that Shield, a new cfDNA blood-based test by Guardant, detected 83% of colon cancers in study participants. However, the test didn't detect precancerous growths as effectively as a colonoscopy.

During the study, 7,861 participants with an average risk for colon cancer had the new blood test and a colonoscopy. After the participants completed both tests, the scientists found that the blood-based test had 83% sensitivity for colorectal cancer, 90% specificity for advanced abnormal cell growth (neoplasia), and 13% sensitivity for advanced precancerous lesions.

For comparison, Cologuard® has an estimated cancer sensitivity of 92%. Still, like the Shield test, its ability to detect precancerous growths and smaller cancers is lower than a colonoscopy. Moreover, in a clinical study, 13% of people without colorectal cancer received a positive Cologuard® result (false positive), and 8% of patients with colon cancer received a negative result (false negative).

In contrast, colonoscopy has a 75% to 95% sensitivity for cancer with an 86% specificity. Health experts consider it the gold standard because doctors can visually examine the entire bowel and remove any suspicious polyps during the procedure.

Since Cologuard® and the Shield blood test only look at markers in stool or blood samples, people with a positive test must follow up with a colonoscopy.


Still, Shield may be more convenient than colonoscopy or Cologuard®, which may help boost screening rates among Americans.

In a Guardant press release, study author Daniel Chung, M.D., a gastroenterologist at Massachusetts General Hospital and Professor of Medicine at Harvard Medical School, said, "More than 3 out of 4 Americans who die from colorectal cancer are not up to date with their recommended screening. The ECLIPSE study results published today support the use of a blood test as a screening option that could help overcome these barriers and improve CRC screening rates."

Recently, Guardant submitted its new blood test for pre-market approval by the FDA. The company says it expects an FDA decision sometime this year.


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