The search for a technique that takes the guesswork out of detecting the extent and depth of cancers has fuelled scientific research projects for a number of decades. Advances in ultrasound, radiology and magnetic resonance imaging technology have all looked promising, but have been less successful for those early tumours which, if spotted in their infancy, could usefully boost the efficacy of treatment. For the last five years a chemical that is found in almost every human cells has been investigated for just such a role — with encouraging results in both the detection and treatment of certain tumours.