Researchers have pinpointed what could be the early genetic origins of breast cancer -- cancer-like mutations appearing in the cells of healthy women. In a new study, the international collaborators analyzed the genomes of more than 48,000 individual breast cells from women without cancer, using novel techniques for decoding the genes of single cells. While the vast majority of cells appeared normal, nearly all of the women harbored a small number of breast cells -- about 3 per cent -- that carried genetic alterations commonly associated with cancer. The findings suggest that these rare genetic anomalies may represent some of the earliest steps in a series of events that could culminate in breast cancer development.