[hecticskeptic]

As I recollect, PSA is useful for tracking Benign Prostatic Hyperplasia....but that’s about it.

[ArmstedFragg]

After surgical removal of the prostate, PSA should fall to zero and stay there, an increase is reason for investigation. Also, after radiation PSA should reach a stable low (nadir) then stay there. (Though there's sometimes a temporary bump) The definition of biochemical failure (the radiation didn't work) uses PSA increases as a reference.

As you indicated, since PSA is nonspecific, BPH or PC or some kinds of infections can all produce PSA increases. You can also have fairly advanced Prostate cancer without a PSA increase.