How Keytrruda's development was accidental, to a large degree. This is a very long article that I haven't finished reading yet but wanted to post for people to read now. Even if you only read the first page, you can see how a blockbuster (and for some cancers, highly effective) drug almost didn't even get developed, much less get to the point of being FDA approved.

https://www.forbes.com/sites/davidshaywitz/20...eb5c71948d