Genetic alterations including somatic mutations are the main cause of cancer and were thought therefore to be exclusively present in cancer cells. These mutations have now been identified in normal cells however, showing a significant association with increasing age. Because a cancer cell develops from a normal cell, we speculated that normal cells adjacent to a tumor may give insights into cancer development. Our study findings reveal frequent somatic mutations in histologically normal tissue adjacent to cancer cells. We found also that pathogenic variants within normal cells tend to clonally expand, which could be linked to cancer development. (By Dr. Chang Ohk Sung, https://jmg.bmj.com/content/early/2020/07/27/jmedgenet-2020-106905 )