I'd tell her, but tell her the truth - and don't allow the conversation to grow beyond what is known. In cricketing terms, it's called playing with a straight bat.
The truth is that you have a slightly raised PSA, which can be due to lots of things, of which cancer is only one. The GREAT NEWS is that you know and it'll be sorted.
Nobody knows what's going on, the consultant will have no clue until he has the results from a scan and biopsy, even if it gets that far. 
Sometimes ignorance is bliss, speculation should be banned, as should google. If necessary, get the dog to eat the router!