Will liquid biopsies transform cancer care?
By David Wahlberg, Wisconsin Health Journalism Fellowship
Developing “liquid biopsies” — blood tests to detect early stages of cancer — involves trade-offs regarding accuracy, the need for follow-up tests, and profitability, speakers said at a Health Journalism 2025 panel on the burgeoning biotech field.
Some liquid biopsies have been around for years, such as the PSA test that detects an antigen that is elevated in prostate cancer but also in some benign prostate conditions. Newer tests are more targeted, finding rare tumor cells circulating in blood or DNA fragments shed by tumors, said Jared Fischer, Ph.D., an assistant professor of molecular genetics at Oregon Health & Science University.
Examples include Shield, a blood test for colorectal cancer by Guardant Health approved in October by the Food and Drug Administration, and Galleri, a test for multiple cancers launched by Grail in 2021.
Fischer and his OHSU colleague Jose Montoya Mira, Ph.D., a translational scientist and bioengineer, in February reported initial success with a blood test they developed for pancreatic cancer, one of the deadliest forms of cancer. Called PAC-MANN, the experimental test caught 85% of pancreatic cancers when used with an older test in a study involving 350 patients. Samples with cancer light up like ghosts from the 1980s video game Pac-Man, Fischer said.
While 85% seems like an impressive rate, deciding who should get such a test is complicated, Montoya said. If 100,000 people in the general population were screened, the test would correctly identify 11 of the 13 people expected to have pancreatic cancer, he said. But it would miss the other two and mistakenly say 2,000 people without cancer had it. Everyone who tested positive would have to undergo expensive follow-up tests, such as MRIs or ultrasounds, to confirm or rule out cancer.
“Who’s paying for that?” Montoya said. “Are you going to convince insurance?”
If the test was given to 100,000 people with a condition that puts them at high risk for pancreatic cancer, it would pick up 12,750 true cancers and yield 1,700 false positives, a much better trade-off, he said. But few people have the condition, so companies wouldn’t have much of a market to make money.
“The least risk of a population you’re looking at, the more profit,” Montoya said.
Liquid biopsies show promise for discovering many cancers earlier than they’re found today, said Jasmine Zhou, a professor of pathology and laboratory medicine at the University of California, Los Angeles. But limitations include a lack of data on their long-term impact on cancer deaths, concern that people might give up standard screenings like mammograms and colonoscopies, and uncertainty about how doctors should validate whether patients who test positive have cancer, said Zhou, co-founder of EarlyDiagnostics, a company developing liquid biopsies.
“Right now, the tests are not perfect,” Zhou said. “The guidance is not clear.”
David Wahlberg is a freelance health reporter in Madison, Wisconsin.
