New blood test for colorectal cancer: what you need to know

For years, the available tools for screening for colorectal cancer were colonoscopies and stool tests. That changed in August, when a newly FDA approved blood tests to detect colorectal cancer became available at doctors’ offices.

Now a new study has spotlighted that blood test, called the Shield Test, and a similar test that has yet to hit the market. The investigation showed that the blood tests can’t happen that much colorectal cancer diagnoses and related deaths as traditional screening methods.

Does this mean that you should not opt ​​for a blood test if you are eligible for colon cancer screening? Here’s what you need to know.

Colorectal cancer develops in the tissues of the colon or rectum and is the third most common cancer in the United States (excluding skin cancer). It is on the rise among younger adults but it is still relatively rare: people under 50 have a 0.4% risk of developing it. Routine screening is recommended by the U.S. Preventive Services Task Force beginning at age 45.

Of the screening options colonoscopies are perhaps the best known and most feared. They involve taking a laxative beforehand to empty the bowels and then a procedure in which a doctor inserts a long, thin tube, equipped with a camera, into the rectum. If no cancer or advanced precancerous lesions called polyps are found, most people can wait ten years before getting another one.

The other screening options are non-invasive, but require more frequent follow-up – and all require a colonoscopy if polyps or cancer are detected.

One option is a CT colonography, also called a “virtual colonoscopy,” which uses X-rays every five years to examine the colon and rectum.

People can also opt for stool testing, which they are also able to do do at home. There are two types: a fecal immunochemical test (FIT), an annual test that uses antibodies to detect blood in the stool, and a FIT DNA test (Cologuard), which looks for blood and altered DNA and is tested every three years is repeated.

The Shield blood test, manufactured by Guardant Health, is the newest screening tool to hit the market. It is intended for people over 45 years of age with an average risk of colorectal cancer. Like the blood test developed by biotechnology manufacturer Freenome, which is seeking FDA approval, it works by detecting circulating DNA that may come from cancers.

A study conducted last year that included nearly 8,000 participants found that the Shield test was 83% successful in detecting colorectal cancer in an average-risk screening population and 13% successful in detecting polyps.

The new Stanford study found that colonoscopies and, to a lesser extent, stool tests are much more effective than the Shield blood test.

To reach this conclusion, researchers used a computerized modeling study to predict the number of colorectal cancer cases and deaths expected if people used each screening strategy (blood tests, stool tests and colonoscopy) over the long term. Uri Ladabaum, MDlead author of the study and professor of gastroenterology at Stanford Medicine.

The team’s projections showed that of the 100,000 people who would have a colonoscopy every decade, 1,543 would develop colorectal cancer and 672 would die from the disease. Those numbers rose for stool-based tests, with researchers finding 2,181 to 2,498 cases per 100,000 people and 904 to 1,025 deaths.

However, of the three screening methods, the rates were highest among people who used the blood tests. Under this projection, CRC cases would range from 4,310 to 4,365, and deaths would rise to 1,604 and 1,679, approximately two and a half times as many deaths as in the colonoscopy group. Blood tests, which can be pricey and not always covered by insurance, were also less cost-effective than other methods, the researchers found.

But blood testing still reduced the number of cases and deaths compared to no screening at all: In that scenario, researchers found that 7,470 people would get the cancer and 3,624 people would die from it.

The research confirms what is already known: colonoscopy is the gold standard for CRC screening. But, as the authors noted, it also sheds light on how the newly developed blood tests work against that.

“The most important conclusion is that first-generation blood tests can provide substantial benefits at an acceptable cost compared to no screening,” Ladabaum said. “But that the currently available stool tests and screening colonoscopy are much more effective and cost-effective.”

The reason blood tests aren’t as effective as other screening tools is that polyps and early-stage cancers don’t release as much DNA as later-stage cancers, said Daniel S. Reuland, MD, a professor of medicine at the University of North Carolina School of Medicine and director of UNC’s Carolina Cancer Screening Initiative Intervention and Implementation Research Program. “Unfortunately, this means that these blood tests tend to detect more later-stage cancers and are not as effective as colonoscopy or stool tests at detecting early-stage cancers or precursors to colorectal cancer,” he told Health.

“This is important,” he continued, “because finding and removing the advanced precancerous lesions can prevent CRC – and reduce its incidence, and finding CRC in its early stages when it is easily curable can reduce mortality of CRC decreases.”

Qin Rao, MDa gastroenterologist at Manhattan Gastroenterology, recommends a colonoscopy for the average person, but a stool test such as Cologuard or CT colonography for people who do not have access to health care or otherwise cannot obtain a colonoscopy.

If you’re switching from one screening method to another, Rao said you should screen for that test at the appropriate intervals. “For example, someone who is told to have a colonoscopy every 10 years should not have a stool test before that 10 year mark if they choose to switch to stool testing in the future,” he said.

That said, it is possible to switch from stool tests to colonoscopies (and vice versa), although this is less common, Rao noted. For example, someone might perform a Cologuard screening every three years, and if it turns positive, perhaps as a result hemorrhoids—then switch to colonoscopies. “Similarly, a person who has been undergoing clean colonoscopies for several years may switch to stool testing later in life to avoid health complications related to the procedure or due to limited access to health care,” Rao said.

So, who should use the newly approved blood tests? Currently, Rao said, these blood tests are only indicated for screening in patients 45 years and older with no family history of CRC. They should not be used in patients at high risk or in patients with alarming symptoms.

Blood tests are not an acceptable substitute for colonoscopies or stool tests, Reuland said, but he said they would be “most beneficial for patients who are not undergoing CRC screening because they have declined both stool tests with FIT or Cologuard and would rather not do so. to get a colonoscopy unless they really need it.”

Because they are less invasive than colonoscopies and can be performed more often, blood tests can also help monitor known cancers or assess risk. Maged Khalil, MDtold a GI oncologist and research associate at the Lehigh Valley Topper Cancer Institute Health.

For anyone interested in going the non-colonoscopy route, Reuland said to keep in mind that a positive test would lead to a recommendation for a colonoscopy anyway: “To be effective, all non-invasive tests require a follow-up colonoscopy if they are abnormal. .”