Experts say it could revolutionize cancer care. It’s called the Galleri test and it can identify cancers before symptoms appear. The UK National Health Service is testing it on 142,000 people. If successful, this trial will be extended to 1 million people next year. Doctors hope 5,000 cases could be detected early as a result. The Galleri test works by identifying changes in bits of free-floating DNA that leak from tumours into the bloodstream.