According to First Trust, an investment house:

There are currently 418 biotechnology medicines either in clinical testing or under review by the Food and Drug Administration, according to a recent report from the Pharmaceutical Research and Manufacturers of America. These medicines target over 100 diseases. The top three therapeutic categories by far are cancer-related conditions (210 medicines), infectious diseases (50 medicines), and autoimmune disorders (44 medicines). A total of 125 biotech medicines are approved for use by U.S. citizens.

The Julian Simon reference is to this.