There is indeed a lot of confusion over this. At one time, cure means you have RP and the cancer is never recurs. Except that is not true. That is why you have recurrence treatment. All other treatment, including hormone is supposed be remission only because sooner or later the disease mutates. Except when it doesnt.
One common fallacy in comparing with other disease mutation is that each subsequent generation gets weaker until it becomes harmless. Influenza for example. Covid 19 is more recent.
The more scientific or cautious statement I have heard is that when you PSA < 0.1 it can be scientifically determined that 99% of the malignant cell is dead. May be more, but that cannot be scientifically determined at this time. However, if there is any, the volume is so small, and the cells are so idle that it would not do any harm for many years. So for all intents and purpose, some doctors will call that a cure.

Dont mind me. I am just another layman trying to make some sense of the whole thing.