Oxford researchers have discovered that blood platelets do far more than help stop bleeding. They also collect and store fragments of DNA circulating in the bloodstream — including DNA released by cancer cells. The discovery could eventually lead to more sensitive blood tests for the early detection of cancer.

Blood platelets are among the smallest components circulating in the human bloodstream. For decades, their best-known function has been straightforward: when a blood vessel is damaged, platelets help form a clot and stop the bleeding.

But researchers at the University of Oxford have discovered that platelets perform another, previously unknown task.

They collect DNA.

An Oxford-led study funded by Cancer Research UK and published in Science has demonstrated that platelets can capture and store fragments of DNA circulating freely in the bloodstream.

Those fragments can include DNA originating from a developing fetus — but also mutated DNA released by cancer cells.

Even more remarkably, researchers were able to identify DNA associated with pre-cancerous conditions inside platelets.

DNA circulating through our blood

Cells in the human body are constantly dying and being replaced.

When cells die, small fragments of their DNA can be released into the bloodstream. Scientists call this material cell-free DNA, or cfDNA.

This circulating genetic material has become increasingly important in medicine.

By analysing DNA fragments in a blood sample, researchers can potentially obtain information about what is happening elsewhere in the body without having to perform invasive procedures such as surgical biopsies.

This principle lies behind the rapidly developing field of liquid biopsy.

But there is a problem.

Most current methods remove the platelets from a blood sample and analyse the remaining plasma.

The Oxford research suggests that, in doing so, scientists may have been throwing away a potentially valuable source of genetic information.

Platelets as DNA scavengers

Platelets do not possess nuclear DNA of their own.

Nevertheless, the researchers discovered that they can take up extracellular DNA fragments circulating through the blood and retain them.

This may serve an important biological function.

Excessive amounts of free DNA in the bloodstream can cause unwanted activation of the immune system and other complications. Platelets may therefore act as part of the body’s mechanism for clearing this material from circulation.

In effect, they behave like tiny DNA scavengers.

But from a diagnostic perspective, what the platelets collect may be just as important as the fact that they collect it.

Finding fetal and cancer DNA

The team, led by researchers at Oxford’s MRC Weatherall Institute of Molecular Medicine, examined DNA contained within platelets.

They found evidence of fetal DNA in the platelets of pregnant women.

They also found mutated DNA in platelets from people diagnosed with cancer.

Importantly, abnormal DNA could also be detected in platelets from individuals with pre-cancerous conditions.

The published research included samples from patients with gastrointestinal cancers, including colorectal, oesophageal and pancreatic cancers, as well as patients with sessile serrated lesions, which can be precursors to colorectal cancer.

A missing piece in liquid biopsies?

This raises an intriguing possibility.

If platelets accumulate DNA originating from tissues throughout the body, analysing them alongside plasma could provide additional information when doctors search for the genetic traces of cancer.

Current liquid-biopsy approaches largely concentrate on cell-free DNA in platelet-depleted plasma.

The Oxford findings suggest that part of the genetic evidence may instead be sitting inside the platelets that have been removed.

Postdoctoral researcher Lauren Murphy, who led the project, said the results indicate that existing liquid-biopsy methods may be overlooking useful genetic information stored within platelets.

Detecting cancer before symptoms appear

Early detection remains one of the central challenges in cancer medicine.

Many cancers are considerably easier to treat when discovered before they have spread. Researchers are therefore developing blood tests capable of identifying extremely small quantities of tumour-derived DNA.

Platelets could potentially increase the amount of information available to such tests.

Professor Bethan Psaila, Professor of Haematology at Oxford and senior author of the study, explained that platelets can carry evidence of DNA damage originating from tissues elsewhere in the body.

That makes them potentially useful as another source of information for cancer screening.

Beyond cancer

The discovery may eventually have implications beyond oncology.

The presence of fetal DNA within maternal platelets suggests possible applications in prenatal genetic testing.

More broadly, if platelets routinely collect extracellular DNA, their contents could provide researchers with a new way of examining genetic processes occurring elsewhere in the body.

A cell fragment previously studied primarily because of its role in blood clotting may therefore turn out to be an unexpected carrier of biological information.

Not a cancer test yet

The discovery does not mean that a new platelet-based cancer screening test is ready for clinical use.

Cancer Research UK stresses that further research is necessary to determine which components of platelet-associated DNA provide the most useful information and how they can be measured accurately.

But the principle has now been demonstrated.

Instead of looking only at DNA floating freely through blood plasma, researchers may be able to examine the genetic material that platelets have collected along the way.

That could add another source of information to the search for cancer at its earliest stages.

For something so small, the platelet may have been carrying a surprisingly large secret.

Source: Based on “Platelets shown to store DNA in study that could transform cancer screening”, published by the University of Oxford on 15 August 2025. The Cancer Research UK-funded research was led by scientists at Oxford’s MRC Weatherall Institute of Molecular Medicine, in collaboration with researchers including teams at the Universities of Edinburgh and Swansea. The underlying paper, “Platelets sequester extracellular DNA, capturing tumor-derived and free fetal DNA,” was published in Science.