An alarm signal from the immune system offers an “invaluable” early warning of returning cancer, research has shown.
Scientists hope the discovery will make it possible to catch recurring cancers before they take hold, increasing patients’ survival chances.
The same team found that rousing sleeping cancers could weaken them and ultimately lead to their destruction by the body's own defences.
Often cancers are successfully treated only to return years later. Breast cancer is especially prone to making an unwelcome comeback - nearly a quarter of women with the disease will experience it a second time within 10 years.
Knowing when a cancer is about to recur would give doctors a valuable head start, allowing them to attack a tumour before it begins to spread.
The main cause of cancer recurrence is small groups of tumour cells that hide away lying dormant, only to re-awaken once they have learned to evade the immune system.
In a study of mice, researchers looked for early signs of an immune response triggered by a dormant cancer waking up. They found that detecting the signal made it possible to predict accurately when a cancer was about to return.
Lead scientist Professor Alan Melcher, from the University of Leeds, said: "The ability to predict when a patient's cancer will come back would be an invaluable tool in treating the disease, allowing doctors to treat the recurrence rapidly and effectively before it takes hold. But we now need to find a way of using this knowledge to develop a test for patients whose cancer could take several years to reappear."
In a surprising twist, the scientists also learned it was possible to force a cancer out of its slumber prematurely. The immune system's defences could then be used to track down the cancer cells and wipe them out.
During the experiments, this approach cured up to 100% of the mice that would otherwise have relapsed. The findings are reported in the journal Nature Medicine.