Can cancer screening reduce the likelihood of developing cancer?

Yes: Decreases incidence and mortality.

Good question: That is certainly the idea behind it. It is hard to say if we are truly successful. Having a pap smear and picking up a lesion before it becomes cancer reduces your likelihood. So does removing a colon polyp before it can become a colon cancer. The problem is that having these things means you are at higher risk in the first place and you need continued watching.