A new blood test may detect cancer recurrence months before scans — but does it save lives?
Doctors are increasingly interested in a new approach to cancer monitoring: personalised blood tests that can detect the return of a tumour long before it shows up on a scan. Known as circulating tumour DNA (ctDNA) analysis, this method looks for tiny fragments of a patient’s cancer DNA in their blood. Proponents say it could transform how cancer is tracked and treated after surgery or chemotherapy. But while the technology is promising, some experts caution that its real-life benefits are still unproven.
What is ctDNA testing?
Every cancer is caused by genetic mutations, and tumours release fragments of their DNA into the bloodstream. ctDNA testing involves sequencing both a patient’s tumour and their healthy cells after surgery, creating a unique fingerprint of the mutations specific to their cancer. Labs then develop a personalised assay to detect even minute traces of this DNA in the patient’s blood.
These tests are sometimes referred to as “tumour-informed” because they target mutations specific to each individual’s tumour. That makes them highly sensitive and, according to researchers, very reliable when used correctly.
How early can they detect recurrence?
In one recent study published in Nature Medicine, researchers found that ctDNA tests identified cancer recurrence in lung cancer patients an average of five months earlier than traditional imaging methods. Similar studies in breast and colon cancer have shown that patients who test positive on ctDNA shortly after treatment are more likely to experience a recurrence, and have worse survival rates overall.
This raises both hope and concern. On one hand, earlier detection could allow doctors to adjust treatment sooner, possibly improving outcomes. On the other hand, it may simply confirm that certain aggressive cancers return quickly — whether or not treatment is altered.
Does it change treatment?
In some cases, yes. One study involving stage II colon cancer patients found that those with negative ctDNA results were able to skip chemotherapy without increasing their risk of recurrence. Those who tested positive received additional treatment. This kind of targeted decision-making could spare patients unnecessary side effects and healthcare systems unnecessary costs.
But this approach is still largely experimental. Outside of clinical trials, most researchers agree that ctDNA testing should be used cautiously. There are no guarantees that acting on a positive result will improve survival. And the emotional burden of learning that cancer may have returned- before any physical symptoms- is another concern.
Is it accurate and approved?
Because ctDNA tests are developed in clinical labs rather than manufactured as over-the-counter diagnostics, they are not subject to the same regulatory approval processes. While they are considered reliable, the U.S. Food and Drug Administration has warned that results can vary between labs and testing methods.
Experts also emphasise that a positive ctDNA result doesn’t always mean a cancer will progress. And even if it does, it’s not clear that earlier treatment always leads to better outcomes.
What are the risks?
Some oncologists worry that widespread use of ctDNA tests could lead to overtreatment. Chemotherapy is taxing, and prescribing it based on microscopic evidence of cancer may not benefit all patients. Studies of imaging-based surveillance in cancers such as breast and lung have shown mixed results when it comes to improving survival. Whether ctDNA surveillance will be different remains to be seen.
The tests also come at a cost: a single analysis for colon cancer, for example, can run to $3,500. And while they may reduce unnecessary chemotherapy in some patients, they might lead others to undergo aggressive treatments earlier than necessary.
What’s next?
Researchers agree that more data is needed. Ongoing clinical trials will help determine whether ctDNA testing truly improves outcomes and whether it should be integrated into routine cancer care.
For now, ctDNA testing remains one of the most exciting developments in cancer surveillance, but it is not yet a magic bullet. As with many medical innovations, the key will be knowing when and how to use it.
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