Realizing the promise of personalized medicine.

Scientific advances have begun to give doctors the power to customize therapy for individuals. However, adoption of this approach has progressed slowly and unevenly because the trial-and-error treatment model still governs how the health care system develops, regulates, pays for, and delivers therapies. Aspinall, the president of Genzyme Genetics, and Hamermesh, chair of a Harvard Business School initiative to improve leadership in health care organizations, discuss the barriers to personalized medicine and suggest ways to overcome them.