There has been a good bit of news laterly about a blood test that can find single cancer cells (not just PCa) in a sample. It is still experimental. It was mentioned in my support group a few weeks ago.
A PCa variety is in development at Armune BioScience, and is called Luminex (had to look that up on line).
There is a moral issue to detecting cancer markers "too early" - if potential employers discover that you will have PCa (or any other cancer, for that matter) years or tens of years before it might be significant or even treatable, the person might never be able to obtain a decent job, and may spend a lifetime worrying about what might come if they manage to never step in front of any of the other "bus-events" in life. Talk about lousy quality of life. Availability of this sort of test will surely be followed by years of arguments over privacy and rights.