Current techniques for studying the genetics of cells within tumours involve taking a sample from the cancerous area and analysing the DNA of those cells. The problem is that many cancers, such as prostate cancer, are three dimensional, which means that any one sample would only give a small snapshot of the tumour. By grouping cells according to similar genetic identity, they were surprised to see areas of supposedly healthy tissue that already had many of the genetic characteristics of cancer. Dr Henry Stennett, Research information manager at Cancer Research UK, who funded the research, said: 'This fascinating research challenges our understanding of how cancer develops. Their results show that apparently healthy cells in the body can have the same DNA damage as cancer cells.