Blood testing is now included in screening recommendations for colon and rectal cancer

By Jacqueline Howard, CNN

(CNN) — The American Cancer Society is adding some new testing options to its screening guideline for colorectal cancers – and for the first time, that includes a blood test.

Colonoscopies are still considered the gold standard for detecting colorectal cancer, which starts in the colon or the rectum. The procedure, performed under anesthesia, allows doctors to closely examine the colon and rectum for warning signs of disease. People who would rather avoid an invasive exam might opt for other visual exams or stool-based tests, which have also remained a widely recommended option, even if the idea of collecting a fecal sample can make some people squeamish.

But many people tend to skip screening altogether because they don’t want to or can’t complete these options, even as there has been a rise in colorectal cancer cases at younger ages.

To help close that gap, the American Cancer Society now recommends another screening option: blood testing.

In an updated guideline released Wednesday, the American Cancer Society has added blood-based screening tests to its list of recommended choices for adults age 45 and older who are at average risk for colorectal cancer and who have not completed or have declined visual exams and stool tests.

The blood-based screening test the group recommends is the Shield test, by the biotech company Guardant Health. It was approved by the US Food and Drug Administration in 2024.

The guideline also includes additional stool-based tests: an upgraded version of Cologuard, called Cologuard Plus, and a new FDA-approved test called ColoSense, which was developed by the biotech company Geneoscopy. Each is an at-home stool test, in which samples are collected at home and sent to a lab, where the test can detect molecular markers associated with colorectal cancer.

Blood test still isn’t the ‘first choice’

The researchers who published these updates in a report in CA: A Cancer Journal for Clinicians wrote that “at this time, blood‐based tests should be recommended only to individuals who decline or do not complete preferred screening tests,” which would be visual imaging exams like a colonoscopy or stool-based tests.

A blood-based test is not the “first choice” because it’s not as sensitive as the other testing options in detecting precancerous polyps, but “I do think it is the right option for the right population of patients,” said Dr. William Dahut, chief scientific officer for the American Cancer Society.

“There are a lot of people who can’t or won’t do a colonoscopy, or the idea of collecting their own stool for testing they just won’t do,” Dahut said. “Having more options hopefully will allow more people to be screened to find cancers earlier on, and we’ll be able to cure more patients.”

Screening can dramatically improve survival if a cancer is diagnosed before symptoms begin, because that means treatment can also start early. It’s estimated that more than 90% of people who detect colorectal cancer at stages I and II will survive at least the next five years.

When cancer is found at a more advanced stage, it may have spread into surrounding regions or other parts in the body, making it more difficult to treat and the patient less likely to survive, regardless of their age.

Getting screened also can help reduce the risk of developing colorectal cancer because almost all colorectal cancers begin as precancerous polyps in the colon or rectum. Through a visual exam, like a colonoscopy, these polyps can be identified and removed before they turn cancerous. Stool tests can also pick up signs of precancerous polyps, and if a stool test is positive, it must be followed up with a colonoscopy, which provides an opportunity for prevention, according to the American Cancer Society.

The updated screening guideline is “very forward thinking and reality based,” said Dr. Ursina Teitelbaum, a professor of gastrointestinal oncology at the University of Pennsylvania and section chief of gastrointestinal cancers at Penn Medicine, who was not involved in the American Cancer Society’s recommendations.

Teitelbaum added that blood-based testing remains another option, “albeit imperfect since it may miss early-stage cancers and precancerous lesions. It all harkens though to ‘perfect’ is the enemy of good and these new guidelines acknowledge the need to broaden the capture of screening, particularly in younger vulnerable populations,” Teitelbaum said in an email.

Although the Shield test is the first blood-based to be recommended, more could be on the horizon, said Dr. Scott Kopetz, a gastrointestinal medical oncologist at The University of Texas MD Anderson Cancer Center.

“This is the first blood-based test but won’t be the last, and the hope is that future tests will continue to reduce the barriers to access to effective screening and will have improved performance. The technology will only improve from here,” Kopetz, who was not involved in the American Cancer Society’s updated guideline, said in an email.

For now, “the blood-based screening does not perform as well for detection of pre-cancer as the other screening options and therefore should be reserved for individuals who will not complete other recommended screening,” he wrote. “Importantly, patients who otherwise would be willing to be screened by colonoscopy, stool-based tests, or other recommended methods should not swap to the blood-based assays.”

What to know about your options

The American Cancer Society recommends three types of colorectal cancer screening tests: blood-based tests, visual exams and stool-based tests.

Dahut noted that the updated guideline and recommendations around the various screening options are only for adults at average risk of colorectal cancer.

Adults who may have a personal history or family history of colorectal cancer or advanced pre-cancer lesions, or other risk factors associated with colorectal cancer, are recommended to talk with their doctor about getting a colonoscopy.

“If you have symptoms of colorectal cancer, potentially – bleeding, pain, problems with your stool, abdominal pain – then the stool and blood tests are not appropriate,” Dahut said. “Then you should go in for a visualization.”

Blood-based tests

Blood-based tests, like the Shield test, involve simply having your blood drawn at a health care facility. To screen for cancer, the Shield test is recommended every three years.

“For individuals whose doctors are seeing that another year has gone by and they have not been screened, the blood-based test is probably the easiest to do because you can walk into your doctor’s office, get the blood and head home,” Dahut said.

The Shield test can detect signals for colorectal cancer from tumor DNA that may have shed into your blood. If it returns a positive result, a colonoscopy is recommended.

Test sensitivity

Clinical trial data shows that the Shield test has around 83% sensitivity for the detection of colorectal cancer, which is the test’s ability to correctly identify someone with the disease, and 90% specificity, which is the test’s ability to rule out whether someone has cancer.

Blood-based tests tend to have lower sensitivity for stage I cancers than stool-based tests and visual exams, Dahut said.

“This test is very good at picking up stage II, stage III and stage IV cancers. It’s not as good at picking up the stage I or the adenomas, the precancers,” Dahut said. “That’s why we still prefer the other tests.”

Cost

The Shield test is a Medicare-covered service, according to its website, with $0 co-pay for most Medicare beneficiaries. The list price is around $1,495.

Visual exams

Visual examinations – including colonoscopies every 10 years, virtual colonoscopies every five years and flexible sigmoidoscopies, which examine only the lower half of the colon, every five years – involve using medical instruments or special imaging tests to look inside the colon and rectum to identify and, in some cases possibly remove, any polyps or lesions that might be cancer or precancerous.

Test sensitivity

Visual exams tend to have high sensitivity. For instance, it’s estimated that colonoscopy can have 95% sensitivity and up to 89% specificity. Potential risks of colonoscopy or other visual exams may include issues with anesthesia, bleeding or infection, but serious complications are rare.

Cost

Although most insurance companies fully cover visual exams for screening, “costs really can vary if a patient has to undergo follow-up exams for additional procedures. In spite of the rules under the ACA, some patients have reported surprise billing,” Dahut said of the Affordable Care Act, which requires both private insurers and Medicare to cover the costs of all colorectal cancer screening tests that are recommended by the US Preventive Services Task Force.

Stool-based tests

Stool-based screening involves collecting a sample of your feces and sending it to a lab to be tested for signs of cancer, such as small amounts of blood or traces of altered DNA or RNA from cells in the stool. These are recommended every year or every three years, depending on the test.

Test sensitivity

With Cologuard Plus, it’s estimated that 95% of adults with colorectal cancer will test positive, a measurement of its sensitivity, and 94% of adults without precancerous polyps or colorectal cancer will test negative, a measurement of its specificity, according to the product’s website. And ColoSense has demonstrated 93% sensitivity for detecting colorectal cancer, according to Geneoscopy, the company behind the test.

Cost

These types of tests are typically covered by insurance, but for people without insurance, they can cost hundreds of dollars.

“For individuals without health insurance, I think out-of-pocket costs for the stool test Cologuard Plus is about $650 or so,” Dahut said, adding that most insurance companies cover all recommended stool tests for colorectal cancer screening.

Deadliest cancer for young adults

The updated guideline reaffirms that average-risk adults should begin colorectal cancer screening at age 45 and continue through 75 for those with a life expectancy of more than 10 years. The guideline recommends that doctors discourage screening in people older than 85 because by that age, the risks outweigh the benefits.

The US Preventive Services Task Force also recommends starting screening at age 45, but it does not include blood-based testing as a recommended screening test. At the time the USPSTF recommendation was last updated in 2021, there was no FDA-approved blood test for primary screening in people at average risk.

The task force’s recommendations guide doctors and inform insurance coverage. It’s unclear whether the USPSTF will follow the American Cancer Society’s decision to recommend blood testing.

The task force has not met in over a year, and US Health and Human Services Secretary Robert F. Kennedy Jr. appears to be restructuring its membership. The USPSTF aims to keep all of its recommendations current by reviewing each topic every five years for either an update or reaffirmation, which means its recommendation on colorectal cancer screening is due for another review.

It’s estimated that more than 90% of people complete screening when they have a blood-based test for colorectal cancer, compared with 28% to 71% of people who complete colonoscopy or stool testing, according to Guardant Health.

“The problem is the participation rate to colonoscopy and stool-based tests is not very high,” said AmirAli Talasaz, co-founder and co-chief executive officer of Guardant Health. “By making colorectal cancer screening more accessible with a blood-based option in conjunction with other established methodologies, we can get more people screened.”

In general, about 1 in 3 adults who are eligible for colorectal cancer screening still have not been tested with any screening option as recommended, according to the American Cancer Society. And colorectal cancer has surpassed other cancer types to become the leading cause of cancer deaths among people under 50 in the United States, as of 2023.

It’s estimated that more than 60% of colorectal cancer patients under 50 are diagnosed after the disease has advanced to stage III or IV.

Dahut said the American Cancer Society has been reviewing its screening guidelines and continues to look at data to evaluate whether the recommended age to start screening should be lower than 45.

“We were one of the first to lower it to 45, and if there’s evidence to lower it to 40 or 42, we’ll certainly be doing that,” he said.

Kopetz, from MD Anderson, said for now “it is reasonable” to start screening at age 45 for average-risk people.

“Unless there is a family history or cancer predisposition syndrome, it is reasonable to start screening at age 45. Research is ongoing to develop screening strategies that may address the growing incidence of early-onset colorectal cancer,” Kopetz said. “There is a hope that future blood-tests may be sufficiently accurate and cost-effective for cancer screening in a population younger than 45 years old, but we do not yet have that evidence or the right test for this.”

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