Washington – London: Europe and the Arabs

The US Food and Drug Administration (FDA) has approved only five tests, each designed for a single type of cancer. Tests capable of detecting multiple types—such as Cancerguard from Exact and Gallery from GRAIL—remain unapproved. According to a report published in November in the journal Cancer, a study revealed that innovative blood tests could reduce the number of stage IV cancers by 45% over ten years in the United States if made available to five million adults.

This effect is only achieved when the disease is detected in its early stages, when it is most responsive to treatment.

However, experts emphasize that these tests are not yet in everyday use, as they have high rates of false positives, and there are still no clear guidelines for integrating them into established diagnostic and treatment plans.

How is cancer detected? This technique—also known as a "liquid biopsy"—analyzes a blood sample to look for cancer markers without touching the tumor. It can detect circulating tumor cells, fragments of DNA, and tiny pieces of cancer cells.

Dr. Carolina Redozzi of Weill Cornell Medical College explains that the idea is similar to "translating a tissue biopsy into blood," making it an easier way to monitor disease progression.

What tests are approved today?

To date, the U.S. Food and Drug Administration (FDA) has approved only five tests, each for a single type of cancer. Tests that can detect multiple types—such as Exact's Cancerguard and GRAIL's Galleri—are not yet officially approved.

Instead, they are used as "developed in vitro tests" (LDTs), a category that is not FDA-approved but is currently used by doctors or telehealth providers. In Britain, the National Health Service (NHS) is conducting a clinical trial called PATHFINDER 2 of the Galleri test, involving 140,000 people. The results are scheduled for publication in 2027, a move that could pave the way for wider adoption in Europe.

The Variation in the Nature of Tumors
Dr. Isolde Brown of the Royal Marsden Hospital points out that doctors have relied on tissue biopsies for decades to make treatment decisions, making it difficult to change clinical practice even with evidence of the new tests' benefits. The lack of standardized criteria also complicates comparing different tests.

In an independent review, Ruth Etzioni of the Fred Hatch Centre found that the effectiveness of the blood test depends on the nature of each tumor. Some tumors remain in their early stages for a long time, increasing the chances of detection, while others progress rapidly to stage four, reducing the usefulness of annual screening.

She notes that the assumptions used in the Cancer study were overly optimistic about the rate of disease progression. All researchers emphasize that any positive result from a liquid biopsy requires confirmation through further testing before treatment begins. Some treatments—such as immunotherapy—rely on assessing the density of immune cells within the tumor, information that cannot be obtained from blood.

False results threaten credibility. Preliminary data from the PATHFINDER 2 trial showed that the Galleri test, despite its high accuracy (99.6%) in ruling out healthy patients, produced false diagnoses in about 40% of cases that suggested cancer.

Researchers warn that this percentage could generate undue anxiety and burden healthcare systems with a series of unnecessary tests.

To reduce these errors, scientists are working to improve the tests by integrating immune cell signals with tumor markers, as well as standardizing laboratory procedures, which could increase accuracy and reduce false results. A trial is currently underway at the Royal Marsden Hospital to test whether a blood test can identify breast cancer patients who do not require chemotherapy after surgery by detecting tumor DNA in the blood even after tumor removal.

Dr. Redozzi says, "We don't currently have a test that combines the required high sensitivity and accuracy, but I am confident that we will in time."