Liquid Biopsy Tests Could Help Treat Pediatric Cancer

A new blood test that uncovers hidden changes inside cancer cells could help doctors find the best treatments for children and young people with cancer.

The test is a type of liquid biopsy, similar to the ones NHS England is rolling out to help diagnose and treat lung cancer and breast cancer in adults. It works like a high-tech fishing net, catching and analyzing telltale scraps of DNA that cancer cells release into the bloodstream.

This circulating tumor DNA (ctDNA) can contain vital information about the mutations driving cancer. By revealing it to doctors, the new liquid biopsy could help them find the best-targeted drugs for young patients whose cancer comes back.

Researchers at the Institute of Cancer Research (ICR) in London developed the test as part of the SMPaeds (Stratified Medicine Paediatrics) program, which we co-fund with Children with Cancer UK. Their first study, published in Cancer Discovery, confirmed that the liquid biopsy can be used alongside traditional tests on small samples of cancer tissue (tissue biopsies) to give doctors a more complete picture of children’s and young people’s cancers. Now the team is moving on to the next phase of the research, where they’ll see if that extra information can help doctors find more effective treatments when the standard options stop working. 

That’s just one of the test’s potential benefits. As liquid biopsies don’t require surgery to directly remove tumor tissue, they’re also much kinder on growing bodies. Although the technology behind it is currently only available in research labs, doctors could one day use the test to keep monitoring patients and tweaking treatments as part of standard care.

The SMPaeds program

Led by Professor Louis Chesler at the ICR, SMPaeds is a precision medicine program focused on finding targeted drugs that can help children and young people when their cancer returns or starts growing again (relapses) after initial treatment.

In its first phase, SMPaeds did that by running genomic tests on tissue biopsies from newly relapsed patients and sending the results straight to doctors. Doctors then used that information to find any new treatments or clinical trials that had the potential to help the children and young people in their care.

Alongside that, the SMPaeds team also investigated their new liquid biopsy testing approach, which makes it possible to do genomic tests of many cancers using blood samples. That work led to the Cancer Discovery paper.

Now, in SMPaeds 2, the team will provide doctors with results from both tests when their patients relapse. From there, ICR researchers will monitor how the extra information from the liquid biopsy helps doctors tailor their treatment decisions.

“We’ve shown that ctDNA offers complementary information to tissue sequencing,” says Dr. Sally George, who led the development of the test.

“For lots of tumors, if there’s enough ctDNA present in the blood, we often find much more information from the [blood] plasma-based sequencing than we find in the tumor biopsy.

“SMPaeds1 has validated that this test that is ready to go, so in SMPaeds2 we will look at the value of reporting back ctDNA test results at the time of relapse or disease progression. This is the first step towards making ctDNA testing more widely available.”

The advantages of liquid biopsies

Liquid biopsy testing can reveal more about cancers because it picks up DNA from cells all across tumors.  

“As you can imagine, if you biopsy one tiny piece of tumor, you might miss the mutation that’s over on the other side,” explains George, who is also a group leader at the ICR and a consultant at the Royal Marsden NHS Foundation Trust. “A liquid biopsy can give us a much broader overview.”  

Testing with a traditional tumor biopsy is a bit like studying an archaeological site by digging one small hole straight down into it. That’s a good way to find out a lot about one particular building, but it probably won’t help you understand how it connects to anything else. The ctDNA test is more like using radar to map out an entire ancient town from above.

Both approaches have their advantages. Some matter more for children and young people. In the same way radar imaging leaves the ground undisturbed, liquid biopsies put much less strain on young patients.

“These patients are often children who require general anesthetic for procedures – small people who go through a lot,” says George. “Their tumors could be in areas that are risky or problematic to get to, and you can’t keep taking tissue from a child. Having less invasive tests that can help us understand how their tumors change is really, really important.”

Powering precision medicine

The initial study of the liquid biopsy has also identified some mutations that become more prominent when certain cancers relapse. Scientists can now use that information to prioritize research into new targeted treatments. 

In the future, George and the rest of the SMPaeds team hope to use their new test to find more changes that we could target with new drugs. Because the test is so much less invasive, there’s also potential for doctors to use it to track tumors and direct treatment in something closer to real-time. 

“This could be a really powerful way of understanding, actually in patients, how treatments change cells,” says George.   

That’s especially important for children and young people, whose cancers are different than the cancers that usually affect adults.  

“One of the reasons why childhood cancers are so difficult to treat is because they are reminiscent of embryonal cells, which can change into lots of different cell types,” George explains. “We can’t currently track how those cells change, but it could be possible to use multiple liquid biopsies to see exactly how they adapt to evade treatments.  

“So, if we find out, for example, that neuroblastoma cells change in a specific way to evade normal chemotherapy, then we can begin to identify new treatments to target those changes.” 

Reference: George SL, Lynn C, Stankunaite R, et al. Stratified medicine pediatrics: Cell-free DNA and serial tumor sequencing identifies subtype-specific cancer evolution and epigenetic states. Cancer Discov. 2025;15(4):717-732. doi: 10.1158/2159-8290.CD-24-0916

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