Could a Blood Test Effectively Screen for Cancers?

The innovation shows promise, but so far, it returns many false positives

A row of blood samples in vials
The blood test screens for over 50 types of cancer, some of which can not be screened for currently. David Silverman/Getty Images

A blood test designed to detect over 50 types of cancer could be a game-changer for diagnosing the disease, researchers say, but it still needs work before being ready for widespread use.

In preliminary trial results, the test found a positive cancer signal in 92 (1.4 percent) of more than 6,000 presumably healthy adults over the age of 50. Of those positives, follow-up testing confirmed cancer in 38 percent, Medscape Medical News’s Roxanne Nelson reports.

The test “is not ready for prime time,” as Catherine Marinac, a co-author of the study and a researcher at the Dana-Farber Cancer Institute, tells U.S. News & World Report’s Amy Norton. But researchers say it has the potential to improve cancer diagnosis down the line.

“As this technology develops, people must continue with their standard cancer screening, but this is a glimpse of what the future may hold,” Deborah Schrag, a co-author of the study and a medical oncologist at Memorial Sloan Kettering Cancer Center, tells Medscape.

Schrag presented the findings, which have not yet been peer reviewed, at a meeting of the European Society for Medical Oncology in France last week.

Cancer is a leading cause of death worldwide. Treatment is more effective when the disease is caught early, but a review published in the journal Science in March found that half of all cancers are already at an advanced stage by the time they’re detected, writes Popular Science’s Laura Baisas.

The hope is that blood tests to detect cancer—of which there are a number in development, per U.S. News—can catch the disease earlier and lead to better outcomes. The test in the new study, called the Galleri blood test, looks for cancer DNA in the blood, per the Guardian’s Ian Sample.

In the study, 48 percent of the detected non-recurrent cancers were found at an early stage, and 71 percent of the patients who were diagnosed had cancers that are not routinely tested for, according to a press release.

“What is exciting about this new paradigm is that many of these were cancers for which we don’t have standard screening,” Schrag tells Medscape.

Still, the test has its drawbacks. While fewer than 1 percent of the study participants received a false positive result, more than half of the positive results given were not confirmed by further testing.

Of those who tested positive, more than 90 percent took a follow-up imaging test, and half had more than one invasive procedure, such as a biopsy, according to Popular Science. Thirty percent of participants who received a false positive had invasive procedures, per the press release.

Though the test did predict the location of the cancer, which helped target follow-up work, doctors were still hesitant to stop diagnostic work for patients who received a false positive result from the blood test, Marinac tells U.S. News. After 79 days, half of the participants who would ultimately be told they had received a false positive result were still undergoing testing. All these follow-up tests can take time, cost a lot of money and provoke stress.

“About 60 percent of patients with a positive test result likely suffered from a considerable amount of anxiety that may persist even after further testing did not reveal a malignancy,” Anthony Olszanski, a researcher at the Fox Chase Cancer Center who was not involved with the study, tells Medscape.

Next year, England’s National Health Service will report results from a study of the blood test with 140,000 participants. The current study was funded by GRAIL, the biotech company that made the test, per U.S. News.

The Galleri blood test is offered by a number of U.S. health networks, according to Medscape. It is not approved by the Food and Drug Administration or covered by medical insurance, so people must pay around $950 to take it.

In the future, further research will be required to show whether detecting cancer with a blood test truly makes the disease less likely to be fatal, Marinac tells U.S. News. It “remains unclear if detecting cancer early will lead to better outcomes,” Olszanski says to Medscape.

Editor’s note, September 21, 2022: This story has been edited to clarify that more than half of the study’s participants with positive blood tests were not diagnosed with cancer upon further examination. It has also been edited to correct the number of participants in the National Health Service study; it is 140,000 patients.