In the last decade, scientific advances have made it possible to diagnose and treat a rapidly growing number of diseases—especially various types of cancer—much earlier and with greater precision than ever before. These developments have vastly expanded doctors’ power to customize therapy, maximizing the effectiveness of drug treatments and minimizing their side effects. That’s the good news. The bad news is that progress in realizing the promise of personalized medicine has been slow and uneven in the United States and the rest of the world. Although science is always ahead of practice in the medical field, the gap today in the area of personalized medicine is inexcusably large.

A version of this article appeared in the October 2007 issue of Harvard Business Review.