Ken Alltucker - USA TODAY

An estimated 52,500 Americans died last year from colon cancer, yet the disease is highly treatable if it's detected early. Primary care and prevention experts from the U.S. Preventive Services Task Force recommend adults 45 to 75 get screened for colon cancer.

The most common test to check for colon cancer is the once-a-decade colonoscopy. However, easier methods that can detect signs of the disease in a person's stool are available. And new prescription blood tests are on the horizon. Researchers and manufacturers say simpler tests like these could encourage more Americans to get tested.

The tests are less invasive and time-consuming than colonoscopies, they're often less expensive and they could improve screening rates. Nationwide, about two out of five eligible adults were not up to date on colon cancer screenings in 2021, meaning they did not know their risk for the second deadliest type of cancer.

“There are a lot of patients who don't want to undergo a colonoscopy or just don't have access to it,” said Dr. Aasma Shaukat, a gastroenterologist at NYU Langone Health.

Two stool tests already available are less expensive and easier to complete than a colonoscopy: Cologuard and the fecal immunochemical test, or FIT. The first of two new blood tests could hit the market in 2024 and could broaden the scope of who gets screened, Shaukat said.

Blood screening could come in 2024

Guardant Health, a Silicon Valley company, has developed a DNA blood test called Shield it says can be prescribed by primary care doctors.

Guardant is seeking approval from the Food and Drug Administration, which has scheduled an advisory committee hearing on March 28.

Last year, Guardant released results from a study of 20,000 adults that showed the Shield test identified 83% of colon cancer cases across all stages of the disease. The study detected all late-stage cancers, while the test detected 55% of stage one cancers and 13% of precancerous polyps and other lesions.

Colonoscopies have the highest detection rate at 95%. Cologuard, which finds high-risk genetic mutations in stool samples, can detect 92% of colon cancers. FIT finds 74% of colon cancers based on a single test, but the test is done annually and might detect more cancers over time.

AmirAli Talasaz, co-founder and co-CEO of Guardant, said the Shield test would be prescribed every three years, more frequently than a once-a-decade colonoscopy.

“As long as the patients take our test every three years, the majority of colon cancer cases are going to get detected at an early stage,” Talasaz said. He noted that the survival rate is better than 90% when colon cancer is detected early.

Talasaz anticipates the test will interest people who haven’t been screened for colon cancer and don’t want to undergo an invasive colonoscopy. In a non-peer-reviewed document presented at a scientific conference, the company cited internal data that showed when a doctor orders the blood test, the patients get test results in more than 90% of cases.

Prevention experts say if doctors order a test, it's important that patients follow through. Patients often delay or avoid doctor-recommended colonoscopies, which require them to stick with a clear liquid diet and take a liquid laxative the day before.

"The best screening test is the one that finally gets done," Talasaz said. "That's really the opportunity − to increase overall compliance for colorectal cancer screening."

Will Medicare, other insurers cover blood tests for colon cancer?

Guardant has sold Shield as a laboratory-developed test on a limited basis to employers and other customers, Talasaz said. The price: $895.

If the FDA clears the test, the next step would be to get Medicare to pay for the test. The federal health program for adults over 65 already has said it would cover blood-based colon cancer screening that meets performance thresholds.

Should the company get FDA approval, Talasaz said Medicare's reimbursement rate "would really impact the way we price the test" but he expects the amount would be a "similar ballpark" to stool-based testing and less expensive than colonoscopy.

The U.S. Preventive Services Task Force, an independent advisory panel that evaluates medical tests, treatments and services, has not evaluated the Shield blood test.

Under the Affordable Care Act, insurers must cover preventive care assigned an “A” or “B” grade by the task force. The task force assigned an “A” grade to colon cancer screening for adults 50 to 75 and a “B” grade for 45 to 49.

ACA plans must cover a screening colonoscopy once every 10 years and the FIT test each year, among other screening tests.

The amount doctors and hospitals charge for a colonoscopy can vary widely. A December study in JAMA Health Forum found that hospitals on average charged a facility fee of $1,530 for a colonoscopy, far more than $989 billed by same-day surgery centers. While the screening test should be covered under the ACA, many patients are billed for extra charges, such as sedation and polyp removal. All charges combined can add up to thousands of dollars.

The Shield test had not yet launched when the task force updated coverage for colon cancer screening in 2021. It typically takes five to seven years for the task force to update screening recommendations. That means Shield and other blood tests likely won't be assessed before 2026.

Freenome Holdings, is evaluating another blood test in a study that will collect blood samples from patients undergoing colonoscopies. The company expects to report results by spring 2024, said Shaukat, the study's principal investigator.

How do new blood tests compare to stool tests?

Experts not affiliated with Guardant are not confident the blood tests will gain traction. They say it will be challenging to make headway with the medical community and consumers slow to adapt to non-colonoscopy screening tests.

FIT, a test that detects blood in the stool, has been available since the late 1990s but did not make inroads with the public until the late 2000s, said Dr. Thomas Imperiale, a professor of gastroenterology and hepatology at Indiana University School of Medicine.

While the test is widely used in Europe, it's been slow to gain popularity in the United States market, outside of large organizations such as the Veterans Administration and Kaiser Permanente.

Experts say non-colonoscopy options will be important in reaching the medical community's goal of achieving a colon cancer screening rate of 80%.

Will blood tests miss polyps?

The medical community will closely watch results from a handful of clinical trials that will compare annual or every-other-year use of FIT tests to once-a-decade colonoscopy. One study is being run by the Veterans Administration.

Imperiale said the Shield test might become an easy option for doctors when they already plan to draw blood for other medical reasons. He is concerned that doctors and patients might not discuss in detail the other screening options as well as the tradeoffs and limitations of the blood test used by itself.

"That (Shield) test is okay for picking up colon cancer, but it's not going to get precancerous polyps, especially the most advanced ones that are very easily removed with a colonoscopy," Imperiale said. "It will not detect them except by serendipity."

The clinical study showed the Shield detected 13% of precancerous lesions.

Shaukat, director of outcomes research at NYU Langone, said she envisions blood tests as a "second choice" behind colonoscopy and stool tests. For example, blood tests might be suitable for adults in their late 40s who are reluctant to get a colonoscopy or take a stool test, Shaukat said.

She said there's "a lot of work to be done" to improve screening among people who are 45 to 49. Tests such as FIT and Cologuard are convenient, she said, and she thinks blood tests might improve screening rates, too.

Dr. Barnett Kramer, a retired director of the National Cancer Institute's division of cancer prevention and a member of the Lisa Schwartz Foundation for Truth in Medicine, said FIT tests are relatively inexpensive and backed by evidence. These stool tests also can be taken at home and mailed to a lab. FIT also doesn't have the onerous prep or potential harms of a colonoscopy.

While blood tests might soon become more widely available, Kramer said they are still unproven.

For blood tests, "there's a fair amount of work to be done in order to achieve the same strength of evidence any of the other tests have already achieved," Kramer said.