New Blood Test for Colorectal Cancer Shows Promise in Early Detection, Study Finds

• A new blood test was found to be 83% effective in detecting colorectal cancer in people confirmed to have the disease.
• Researchers were able to detect cancer signals in the bloodstream by identifying circulating tumor DNA (ctDNA).
• The colonoscopy is still the gold-standard for CRC detection.

On Thursday, a Food and Drug Administration (FDA) panel confirmed the safety and efficacy of a new blood test that detects colorectal cancer (CRC).¹

After reviewing evidence, the advisory panel voted that the Shield Blood Collection Kit, made by Guardant Health, was safe, effective, and that the benefits outweighed the risks.²

The decision was, in part, based on research published in March in the New England Journal of Medicine, which showed that the blood test correctly detected CRC in 83% of people confirmed to have it.³

In addition, researchers found that the blood test’s detection rate was similar to that of at-home stool tests—though not as high as that of the gold-standard colonoscopy. For 10% of participants, the blood test falsely gave a positive result when the colonoscopy found nothing.⁴

“We undertook this study to prevent colorectal cancer-related deaths and sought to do this by addressing the need to improve compliance with CRC screening,” William Grady, MD, study author and gastroenterologist at Fred Hutchinson Cancer Center, told Health. “People tend to prefer blood-based screening tests over other types of screening tests, like colonoscopy and stool tests, so we set out to create such a test for CRC.”

Despite the overall positive response from the FDA panel, the experts still had questions and concerns regarding the new blood test.

“This is something that I think patients can adhere to a little easier,” panelist Vikesh Singh, MD, director of the pancreatitis center at Johns Hopkins Medicine, said during the meeting. “[But] is it good enough to go home and say, ‘Look, I don’t have a problem, I don’t need a colonoscopy?’ I’m not so sure it can provide that reassurance.”

Colorectal cancer, which originates in the colon or rectum, is the third most diagnosed cancer in adults in the United States. Early detection could prevent more than 90% of colorectal cancer–related deaths, the researchers wrote. Yet more than a third of the screening-eligible population—those aged 45 to 75—isn’t up to date with screening. 

The most common screening options currently include colonoscopies and stool tests. “We know that the more screening test options people have, the more likely they are to participate in cancer screening,” Grady said.

Finding Colorectal Cancer in Blood

For the study, researchers tested the blood of about 7,800 people at average risk of CRC, meaning they had no family or personal history of the disease, nor did they have inflammatory bowel disease (IBD) or any genetic syndromes putting them at an increased risk.

Guardant Health’s Shield test detects cancer signals in the bloodstream by identifying the presence of circulating tumor DNA (ctDNA)—fragments of DNA that cancer cells release.  

“We can confirm that these fragments of DNA come from cancer cells because of the unique mutations that are only present in the cancer cells and absent in other healthy tissues in the body,” Alisha Bent, MD, an assistant professor of gastrointestinal medical oncology at the University of Texas MD Anderson Cancer Center who was unaffiliated with the study, told Health. “When this test is used in patients with colorectal cancer, it is specific for that tumor and will not detect other cancers.”

The team found that the blood test’s sensitivity was 83%, and the specificity—or ability to find a negative result in disease-free people—was 90%, according to Grady.  

He said the results are similar to those of two types of stool tests. For example, one type of stool test, called FIT, has a sensitivity rate of 76% and a specificity rate of 85%. The rates for Cologuard, another type, are a bit higher, at 92% for sensitivity and 90% for specificity. 

While the blood test represents another early-stage detection option when a colonoscopy isn’t feasible, Grady said colonoscopies are still the best way to detect colorectal cancer, and even prevent it.

And if a blood test does come back positive, people would still need to undergo a colonoscopy to see if they have precancerous lesions, which the blood test can’t typically detect.

“Colonoscopy is the gold standard screening test for colorectal cancers that allows physicians to directly visualize the entire colon and rectum and remove tumors or polyps that may turn into cancer in the future,” Bent said.

What’s Next for Detection

Though some people with colorectal cancer may have symptoms such as fatigue or changes in bowel habits, others won’t have any symptoms. That’s one reason why it’s so crucial that people screen for CRC, Grady said.

He hopes the availability of a blood test will spur people to get screened more often, given that so many currently forego screenings. “At this time, when people are given the option of CRC screening with a stool-based test or with colonoscopy, half of the people are electing to do neither,” Grady said.

While a healthcare provider can order the blood test, it’s not likely to be covered by insurance.

Though the expert panel called for more research on the long-term safety and efficacy of the Guardant Health CRC blood test, the majority “yes” vote likely means the test will be FDA approved in the future. The FDA does not have to follow the advice of its advisory committees, though it usually does.⁵

Guardant Health is expecting an announcement from the agency sometime in the second half of 2024, said Grady.