[PeterisP]

Doctors aren't liable for failing to predict the future or making imperfect diagnosis.

If a doctor reviews the available data, reasonably concludes that it shouldn't be pursued further, and it later does turn out to be cancer, then that by itself does not mean that the doctor is liable for anything. Malpractice requires actual culpable negligence, such as missing something obvious, not interpreting a questionable situation in a manner that turns out to be wrong. The existence of a second, contrary opinion doesn't change that.