More recently, some public-health groups have changed their advice, saying most women can begin mammograms at age 50. In order to refine our understanding of who should start screening when, Dr. Laura Esserman, a breast-cancer expert at the University of California, San Francisco, will lead the WISDOM study, which will test a more targeted approach. About 100,000 women across the U.S. will be randomly assigned to either a personalized screening regimen–determining when to have mammograms according to a woman’s individual risk–or to annual mammograms. Their outcomes will provide insight into whether the current universal recommendations need an overhaul.