A magnetic wire used to snag hard-to-capture tumour cells from blood vessels could prove to be a swift and effective tactic for early cancer detection, scientists say. The wire, which is threaded into a vein, attracts special magnetic nanoparticles engineered to glom onto tumour cells that may be roaming the bloodstream if you have a tumour somewhere in your body. With these tumour cells essentially magnetised, the wire can lure the cells out of the free-flowing bloodstream using the same force that holds family photos to your refrigerator. The technique could even help doctors evaluate a patient's response to particular cancer treatments: If the therapy is working, tumour-cell levels in the blood should rise as the cells die and break away from the tumour, and then fall as the tumour shrinks. "It could be useful in any other disease in which there are cells or molecules of interest in the blood," said Sam Gambhir, a professor at Stanford University in the US. "For example, let's say you're checking for a bacterial infection, circulating tumor DNA or rare cells that are responsible for inflammation in any of these scenarios, the wire and nanoparticles help to enrich the signal, and therefore detect the disease or infection," he said. Cells that have sloughed off the tumour and cruise the bloodstream freely, otherwise known as circulating tumour cells, can serve as cancer biomarkers, signalling the presence of the disease. Circulating tumour cells are often scarce, and a blood draw only samples a few millilitres of the total blood volume, which in adult humans is about five litres. It would be like searching for a grain of sand in a bathtub, but only scooping out a few cups of water. For the magnetic wire, which is about the length of your pinky finger and the thickness of a paperclip, to work, circulating tumour cells must be effectively magnetised with nanoparticles. The nanoparticles contain an antibody that latches onto circulating tumor cells. Once the floating tumour cell and nanoparticle are hitched, the cell lugs the tiny magnet around with it, and when the cell-magnet complex flows past the wire, it's compelled by magnetic force to veer from its regular path in the bloodstream and stick to the wire. Then, the wire is removed from the vein, and the cells are stripped for analysis. Researchers are yet to try out the wire in people, as they still have to file for approval from the Food and Drug Administration, but they have successfully tested it in pigs. "We estimate that it would take about 80 tubes of blood to match what the wire is able to sample in 20 minutes," Gambhir said. It is not practical to remove 80 test tubes of blood from one person - that is more than a half-litre. "So, we're hoping this approach will enrich our detection capability and give us better insight into just how rare these circulating tumour cells are, and how early on they exist once the cancer is present," he said.