One old trope was that we were spending far too much money on HIV research, compared with cancer, given its prevalence in the population. Understanding the science changes your perspective on this. Many of the techniques and insights acquired in the fight against HIV are extremely useful for understanding and mastering other diseases. And sometimes, the drugs developed worked for both. AZT was originally a cancer drug. In combination, it remains a tool against HIV. And now protease inhibitors are showing promise against cancer. It's win-win.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.