A simple blood test may in future provide breast cancer patients with an early warning of the disease returning after chemotherapy and surgery.
The test uncovers small numbers of residual tumour cells that have evaded treatment by detecting cancer DNA in the blood stream.
It is so sensitive that relapses can be predicted several months before new tumours show up on hospital scans. Scientists hope the test will also make it possible to identify genetic mutations likely to prove lethal to some patients, so therapy can be tailored accordingly.