Promising 'Liquid Biopsies' May Not Be Ready for Primetime
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An emerging technology seeks to help revolutionize the world of cancer diagnosis: Multi-cancer early detection tests aim to spot signals for different types of cancer from a single blood draw or other body fluid sample. Also known as a specific type of liquid biopsy, MCED tests look for abnormalities that may indicate cancer, like circulating tumor DNA; some tests can indicate the likely origin of a cancer, while others may merely show that cancer could be present without identifying a probable type or location.
A key advantage of MCEDs, supporters say, is their potential to identify cancers at earlier, more treatable stages. As such, they may help save lives.
CROSS SECTIONS: Dissecting the contentious and the controversial — with science at the core.
Industry tests show some promise: In simulation model research funded by Exact Sciences — a Wisconsin-based company that developed an MCED called Cancerguard — supplemental MCED testing led to an increase in Stage I, II, and III diagnoses (by 10, 20, and 34 percent, respectively). Stage IV diagnoses, meanwhile, decreased by nearly half. The authors — some of whom are listed as employees of Exact Sciences — suggested that this shows MCED testing could catch cancer before it’s at its most advanced stages, particularly for cancer types that lack routine screening.
But while some physicians say the tests are beneficial for people at high risk, some researchers have expressed concern that routine use by asymptomatic individuals without clear risk factors could lead to unnecessary tests and procedures. H. Gilbert Welch, for example, an internist and researcher affiliated with the Brigham and Women’s Hospital’s Center for Surgery and Public Health and a longtime expert on cancer screening, maintains that different types of screenings, including MCEDs, can detect indolent cancers that would rarely cause symptoms or death. In turn, this may result in unnecessary treatments, increased healthcare costs, and patient anxiety. An Australian researcher also points to breast and thyroid cancer as being overdiagnosed. (At least one simulation model, discussed below, suggests the risk for overdiagnosis to be relatively low though.)
MCEDs may also be less sensitive in detecting early-stage cancers, compared to other organ-specific cancer tests, which raises questions as to whether MCED screening actually results in patients living longer. Sensitivity rates — the rate at which a test accurately detects cancer — can be as low as around 20 percent, though they vary widely depending on cancer type and the specific test deployed.
Could more screening be turning mainly healthy people — sometimes called the “worried well” — into patients? It’s possible.
MCED tests, though, do have high specificity, or the ability of a test to correctly identify people without cancer. But when screening a large, mostly healthy population, even a highly specific test can generate numerous false positives. In turn, this can lead to what clinicians call a “diagnostic odyssey,” involving additional blood tests, scans, and biopsies to make a proper diagnosis. In one 2023 study, 62 percent of positive results were false where no cancer was found after an extensive workup.
Could more screening then be turning mainly healthy people — sometimes called the “worried well” — into patients? It’s possible. The late professor of medicine at the University of Pennsylvania, William Kissick, once wrote, “a healthy individual can be defined as someone who has been inadequately studied.” This aphorism jibes with the idea that the harder one looks for a disease, the more incidence one may find.
Multi-cancer early detection tests are not yet approved by the Food and Drug Administration, but they are commercially available to consumers who have a prescription from a qualified healthcare provider. The Galleri test is one prominent example. The product’s manufacturer, Grail, states the test can screen for more than 50 types of cancer at a list price of $949. And Grail says that it sold 185,000 tests in 2025. While most health insurers don’t currently cover the diagnostic, more could...