Last week the big news was that the PSA blood test did not reduce deaths from prostate cancer. How could that be? What happened to the line: 'early detection is the best prevention?' 

It turns out that 'early detection is the best prevention' may not be true for prostate cancer or breast cancer...and maybe others. Why? Because all cancers are NOT the same, and the cancers more likely to be found by screening with PSA or mammograms are the slower growing ones. It's like having a security guard who circles a building once an hour. A fast crook who could get in and out of the building in ten minutes would likely get away with it, while one that took two hours would be likely to be caught.

Screening finds more slow-growing cancers, some of which would never become important or could go away by themselves. We need to not just look for cancers, but the conditions that make them grow -- or make them aggressive -- if we are going to save more lives.