Here's one. I'm sure you can find others ("terminated for benefit"). For statistical reasons, terminating a trial for benefit is relatively uncommon (most terminations occur for other reasons):

https://www.ahajournals.org/doi/10.1161/CIRCHEARTFAILURE.111...

Here's an article on the ethics of a placebo-controlled trial in the first place. It's complicated.

https://acrpnet.org/2018/12/06/ethical-deliberations-on-usin...