[mrosett]

Checkpoint inhibitors (which are the primary driver of improved cancer treatment over the last 15 years and generate > $50B/year in sales) generally don't look very good preclinically. Even their clinical data can be hard to interpret prior to a large scale trial, which led to them almost being shelved.

The catch here is that only two targets (PD(L)-1 and CTLA-4) turned out to work well in humans. All of the other immunotherapies that looked mediocre preclinically turned out to also be mediocre or entirely ineffective in humans.