You're leaving out all choices in your decision pipeline.

If you screen positive, you can elect to have a biopsy or scan.

If your results come back inconclusive, you can elect to pursue surgical (or other) intervention.

That's what medicine is: a selection from among potential procedures, given the information at hand, informed by previous outcomes in similar or applicable situations.

In this case, we simply have more information. If said information turns out to have limited predictive power on the ultimate occurance of cancer, that will be incorporated into detection and treatment practices.

But the important thing is having more information than we had before.