Any commonality in present in varied types of cancer is important, as it provides a potential path to a comparatively low-cost, robust suite of therapies that work for many cancers - and a robust cancer cure is an important component of any future rejuvenation biotechnology toolkit. Here researchers add some weight to the cancer stem cell hypothesis: "Cancer researchers can sequence tumour cells' genomes, scan them for strange gene activity, profile their contents for telltale proteins and study their growth in laboratory dishes. What they have not been able to do is track errant cells doing what is more relevant to patients: forming tumours. Now three groups studying tumours in mice have done exactly that. Their results support the ideas that a small subset of cells drives tumour growth and that curing cancer may require those cells to be eliminated. It is too soon to know whether these results - obtained for tumours of the brain, the gut and the skin - will apply to other cancers, [but if they do], there is going to be a paradigm shift in the way that chemotherapy efficacy is evaluated and how therapeutics are developed. ... Underlying this scenario is the compelling but controversial hypothesis that many tumours are fuelled by 'cancer stem cells' that produce the other types of cancer cell, just as ordinary stem cells produce normal tissues. ... The papers provide clear experimental evidence that cancer stem cells exist ... They have made a major contribution to validating the concept of cancer stem cells. ... Researchers are already busy hunting for ways to kill these cells; now they have more tools to tell whether such a strategy will work."