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- The American Cancer Society now recommends blood tests for colorectal cancer screening.
- The Shield test by Guardant Health is advised for those declining other screenings.
- Blood tests are less sensitive but offer a non-invasive option for reluctant patients.
ATLANTA — 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 cancer is diagnosed before symptoms begin, because 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 can also 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.
Colon cancer leading cause of cancer deaths under 50: When to see a doctor and get a colonoscopy
Colorectal cancer is now the leading cause of cancer-related death for both men and women under age 50 in the U.S.Although the Shield test is the first blood-based test 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."
