A novel blood test for colorectal cancer screening appears effective in clinical trial data, but questions remain about how it can be utilized.

Colorectal cancer screening has a reputation for being difficult, but a new type of screening could make the process as easy as giving some blood. It could even be done during a regular check-up with your doctor.

It’s effective too, but with some caveats. In a study published this week in The New England Journal of Medicine, researchers found that a type of blood test known as a cell-free DNA blood-based test or cfDNA test was able to detect colorectal cancer in 83% of patients who had the disease. The study was funded by Guardant Health, the maker of the test.

The detection rate is similar to an already widely used at-home screening test known as a fecal immunochemical (FIT) test, which is accurate in about eight out of 10 cases.

Colonoscopies remain the “gold standard” for colorectal cancer detection and prevention but require significantly more time, scheduling, and preparation. A colonoscopy is able to accurately identify colorectal cancer in about 95% of cases.

Experts told Healthline that the combination of accuracy and accessibility could be a game changer for screening.

“It’s very, very exciting. I think this has real potential to reshape the entire landscape of colon cancer early detection,” Dr. Christopher Chen, an Assistant Professor of Oncology and Director of Early Drug Development at the Stanford Cancer Institute, Stanford Medicine, told Healthline.

Dr. Ben Park, MD, PhD, Director of the Vanderbilt-Ingram Cancer Center at Vanderbilt University, told Healthline, “It’s studies like these that we really need to move the needle forward and demonstrate that there is validity, or what we call clinical validation, of a test like this. It’s not perfect, as probably everyone can read from the numbers, but it’s a big start.”

Park was not affiliated with the research but disclosed that he is currently engaged in separate clinical trials involving Guardant Health.

The results of the study come from a large, multi-center trial known as the ECLIPSE trial. Some 8,000 patients between the ages of 45 and 84. Participants were at average risk for colorectal cancer and were already undergoing routine screening for colorectal cancer.

The trial tested the effectiveness of Guardant Health’s Shield blood test compared to colonoscopy. Sixty-five participants in the trial had confirmed colorectal cancer from a colonoscopy. The cfDNA test positively identified cancer in 54 of 65 (83.1%) of those participants.

What the test does not do is test for precancerous lesions or polyps, which can develop into cancer. For precancerous lesions, the test only detected about 13% of cases.

“This test is not cancer prevention,” said Chen, “That’s an important distinction.”

Cell-free DNA blood-based tests work by detecting small DNA fragments in the blood that may be emitted by tumors or other cancerous tissue.

“I think it’s really one of the first tests that are using, for blood at least, not just mutations, but a combination of mutations and what we call, epigenetic marks or methylation of DNA as another marker for detecting cancer,” said Park.

Finding those small shreds of DNA is no easy task either, which is part of why cfDNA tests haven’t made a major breakthrough yet in screening colorectal cancer.

“It’s been actually known for decades that all of the cells in our body shed or secrete this naked free floating DNA… so the challenge, even though we’ve known about this for decades, is that the technology didn’t exist for us to really be able to sift through and pick the needle out of the haystack,” said Park.

Colorectal cancer is the second-leading cause of all cancer-related deathsTrusted Source. Despite how deadly the disease is, many adults do not adhere to recommended screenings. Less than 60%Trusted Source of adults ages 45 to 75 receive those screenings, even though these screenings could prevent an estimated 35,000 deathsTrusted Source (nearly 70%) annually due to colorectal cancer.

“With a screening test, you’re testing otherwise healthy people. It’s a hard concept for people to grasp,” Dr. Robert SmithTrusted Source, PhD, Senior Vice President of Early Cancer Detection Science at the American Cancer Society, told Healthline.

While colonoscopies are incredibly accurate at detecting precancerous lesions and colorectal cancer, many simply will ignore them because of the hassle.

The appeal of the cfDNA blood test is that, even with less accuracy, getting more patients to regularly screen for colorectal cancer could be a net positive.

“A test that a patient never receives is never going to be effective. The potential for this to be adopted much more widely is still a very positive step forward, even with certain limitations to its utility,” said Chen.

“Would we prefer to stand on principle and say there’s less expensive, more accurate tests? And by the way, people commonly don’t do them, so we have a lot of people dying from colorectal cancer because they won’t get tested. Or do we capture the patient in the office and essentially make getting screened pretty simple and pretty appealing?” said Smith.

“We’re fairly loyal to the most accurate test. But it may be that the most accurate test is the test that a sizable fraction of the population will use,” he said.

A new blood test is able to detect colorectal cancer in about 83% of cases, similar to some at-home screening tests.

Colorectal cancer is one of the most deadly forms of cancer, but not enough adults regularly screen for it.

Experts believe the new test could help bridge the gap of accessibility and get more adults screened regularly.