A Promising New Blood Test for Colorectal Cancer Is in the Works—Here’s What You Should Know

Katie Camero
·6 min read

celsopupo/Getty Images/Amanda K Bailey

Colorectal cancer has been in the news a lot lately, and rightfully so. On one hand, rates are dropping in older adults thanks to better screening. But on the other, more younger folks are developing the disease, and experts aren’t sure why. One thing is clear, though: A lot of adults who should get screened for colorectal cancer just…aren’t. In fact, about 50 million people ages 45 and older aren’t up to date with their recommended screening, according to the American Cancer Society.

A new type of screening method, however—one that doesn’t involve scooping poop into a cup (gross) or a procedure that requires general anesthesia (we’re looking at you, colonoscopies)—could soon earn the FDA’s stamp of approval and maybe boost people’s willingness to get screened for the disease.

The “Shield” blood test, developed by California-based biotechnology company Guardant Health, can detect colorectal cancer in people at average risk of the disease, according to a study published in March in The New England Journal of Medicine (NEJM). The Shield test is currently available via prescription for a hefty $895. Medicare and most private insurance companies require FDA approval before they consider covering such things, a Guardant spokesperson tells SELF, so until then, you’ll have to pay out of pocket for it.

An FDA advisory panel of experts met last week and voted in favor of the test’s safety and effectiveness, concluding that the benefits outweigh the risks for the people it’s intended for. The FDA—which usually listens to such panels, but not always—still has to decide whether to approve the test, a decision that the Guardant spokesperson says is expected later this year.

Despite some of the test’s limitations, GI experts we talked to are happy about potentially having another option to help screen people. “Colon cancer is the second leading cause of cancer death in men and women in the US, and even with existing tests, people still don’t get screened,” Douglas Corley, MD, PhD, a gastroenterologist and chief research officer with Kaiser Permanente Northern California Division of Research, tells SELF. “So any test that can make it easier for people to get screened is a big deal.”

Here are the most important things to know about the Shield colorectal cancer blood test.

How does this blood test work?

Like any other lab work, you can get the Shield test during a regular medical visit, as long as your doctor ordered it. The analysis looks for tiny pieces of DNA that colorectal cancer tumors dump into your bloodstream. You’ll receive an “abnormal” or “normal” result in about two weeks.

Who is this blood test for?

The Shield test is intended only for people ages 45 or older at average risk of colorectal cancer, which is the recommended age to begin screening if you’re in that group. This means the Shield test isn’t an option for high-risk people of any age, including those with a personal or family history of colorectal cancer, people who have inflammatory bowel disease, and those with a known genetic condition like Lynch syndrome. Those people are more likely to have cancer or polyps that can become cancerous, so it makes more sense for them to get a colonoscopy sooner rather than later, Dr. Corley says.

Can this blood test actually detect colorectal cancer?

It can, but experts advise interpreting its results with caution. An “abnormal” reading suggests—but does not confirm—you have colorectal cancer or precancerous polyps that have a high chance of turning into cancer. In this scenario, you’ll have to follow up with a colonoscopy. A “normal” reading suggests you don’t have any of the above, but the company says it does not guarantee you’re cancer-free and that you “should continue participating in guideline-recommended screening programs.”

The NEJM study of nearly 8,000 people aged 45 to 84 showed that the blood test was pretty good at picking up stage 1, 2, and 3 colorectal cancers, but was not as accurate for advanced precancerous polyps. Dr. Corley explains that smaller polyps can sit on top of the lining of your colon “like a mole on your skin,” so they don’t invade or leak much (or any) of their DNA into blood vessels, which can help explain why the test isn’t great at finding those early growths.

Meanwhile, the test had about 90% specificity for advanced colorectal cancer or precancerous polyps, which means that most of the time it can tell when people actually don’t have the disease. This is particularly comforting considering how stressful a false positive can be, Dr. Corley says.

This blood test still isn’t as effective at catching colorectal cancer compared with other screening methods like a colonoscopy or stool exam, he adds, but like we already mentioned, getting people screened at all is the ultimate goal. “If we detect colorectal cancer early, we have really good ways of being able to treat it and save people from dying,” Dr. Corley says. “But that's not the case if you detect it late.”

Why this colorectal cancer blood test could be a big deal

There are a number of blood tests in the works that are designed to detect different cancers, some that are already available and some that are not. The Shield test, in particular, shows a lot of promise. “This is one of the first blood tests using this technology that's seeking FDA approval and actually has evidence that shows it works,” Dr. Corley says. “It’s also one of the only ones to focus on a single organ and type of cancer; other blood tests being studied are trying to detect multiple types of cancers, which is a more complex thing to get FDA-approved.” (These two blood tests are FDA-approved for people already diagnosed with solid cancers and are used to help guide treatment decisions.)

If the FDA does approve it—a step that would make it much more accessible for people—colorectal cancer screening rates could skyrocket, Dr. Corley says, and as a result save thousands of lives. In one 2018 study, about 76% of colorectal cancer deaths occurred in people ages 55 and older who were not up to date with recommended screening. Another study Dr. Corley worked on found that higher screening rates cut colorectal cancer deaths by more than 50% from 2000 to 2015. Even more impressive: Data suggests that better screening can, over time, reduce racial disparities; Black people are more likely to develop and die of colorectal cancer than other folks in the population, Dr. Corley says.

It really comes down to convenience, he admits, because if people can get a better picture of their colorectal cancer risk without having to handle their poop or take time off of work for a colonoscopy…they will. “If this offers an option to a person who would not otherwise get screened, then it’s a good thing,” Dr. Corley says. “The best test is the test that gets done.”

Related:

Originally Appeared on SELF