'Exciting' blood test spots cancer a year early.
Doctors have spotted cancer coming back up to a year before normal scans in an "exciting" discovery.
It should allow doctors to hit the tumour earlier and increase the chances of a cure.
They also have new ideas for drugs after finding how unstable DNA fuels rampant cancer development.
The research project was on lung cancer, but the processes studied are so fundamental that they should apply across all cancer types.
Blood testIn order to test for cancer coming back, doctors need to know what to look for.
In the trial, funded by Cancer Research UK, samples were taken from the lung tumour when it was removed during surgery.
A team at the Francis Crick Institute, in London, then analysed the tumour's defective DNA to build up a genetic fingerprint of each patient's cancer.
Then blood tests were taken every three months after the surgery to see if tiny traces of cancer DNA re-emerged.
The results, outlined in the journal Nature, showed cancer recurrence could be detected up to a year before any other method available to medicine.
The tumours are thought to have a volume of just 0.3 cubic millimetres when the blood test catches them.