Our body comprises up to sixty trillion cells, all of which are derived from one fertilized egg. Each cell in our body faithfully inherits genetic information through the cooperation of a number of elaborate mechanisms. In contrast, most cancer cells show chromosomal abnormalities and genetic mutations, which are caused by genomic instability, a condition in which the mechanisms ensuring faithful transmission of genetic information are impaired. Genomic instability is also reported to be seen in Alzheimer’s disease and aging, although the underlying mechanisms are not fully understood. We are investigating how genomic instability occurs, and how it is related to cancer and aging. Through these approaches, we are aiming to develop a strategy to prevent disease by increasing genome stability, and to develop cancer therapies by targeting genomic instability.