Blood test could detect cancer returning months before a scan, researchers have found
A blood test may be able to detect signs of cancer returning months before it can be seen on a scan, researchers have discovered.
The test, called a ‘liquid biopsy’, detects tiny fragments of circulating tumour DNA, or ctDNA, in the blood and looks for genetic changes linked to cancer.
Researchers reviewed evidence from dozens of previous studies and clinical trials on ctDNA.
They found that ctDNA can sometimes show if treatment is working, identify mutations that could help doctors choose next steps and detect tiny amounts of cancer left in the body.
The researchers said an early rise in ctDNA could allow doctors to change treatment ‘before tumour progression is detectable with conventional imaging’.
In one study of 130 people with bowel cancer, ctDNA detected signs of the disease returning nearly nine months earlier than standard imaging.
The test could also help some patients avoid unnecessary chemotherapy.
In one bowel cancer trial, patients whose treatment was guided by ctDNA had similar outcomes to those receiving standard care, while fewer received chemotherapy.
A blood test could detect the return of cancer months before a scan, researchers have found
The researchers stressed that ctDNA is not a perfect test. Some cancers release very little DNA into the bloodstream, meaning the test can miss cancer.
It is also unclear how doctors should respond when ctDNA detects cancer but scans show no disease.
The researchers said: ‘ctDNA may help select the best treatment and timing of therapy for a patient with cancer, but optimal clinical applications remain unclear.’
They also warned in the review, published in the medical journal Jama, that a negative ctDNA test does not necessarily mean that a genetic change is not present in the cancer itself.
Liquid biopsy testing is already available through the NHS for eligible lung cancer patients and for specific genomic testing in breast cancer.
NHS England says the approach can speed up access to targeted treatment, with some lung cancer patients receiving treatment decisions around two weeks earlier than usual.
