If you still have the diagnosis letters, check whether he was diagnosed with adenocarcinoma or a different kind of prostate cancer. There are at least 27 different kinds and some do not produce PSA, some do not respond to hormone treatment in the way that most would, some are more likely to spread to organs rather than bones, etc. If your OH has a rare type, it is helpful to know which one as that helps you to understand why some treatments haven't worked very well.
If you don't have a copy of the diagnosis letter, you could ask at the GP surgery what type of prostate cancer it is.