I think there is some confusion about how your relative's cancer developed or he did not make his family aware of all the details at the time - perhaps he didn't want to worry you. You say that he didn't know it had spread until Feb 2019 and then in July 2019 it had'nt spread but that isn't possible. Also, he can't have been on Enzalutimide for all those years because it hadn't been invented then and it isn't used unless the normal hormone treatment has failed.
Reading between the lines, my best guess is:
- he had the op about 12 years ago
- it wasn't successful in removing all the cancer which had already spread and so he was started on hormone treatment (possibly Zoladex?)
- the fact that he didn't have curative RT all those years ago suggests that they knew even then that the spread was outside his prostate bed
- possibly, in 2017 he had a hormone holiday OR he was started on Enzalutimide because the Zoladex had stopped working & the cancer was progressing
- if started, the Enzalutimide was then stopped - either because it wasn't working or he was struggling with the side effects?
- in Feb 2019 a scan showed that the cancer had progressed in his spine and he was given a shot of palliative radiotherapy to stabilise the spine & reduce pain
- they re-started the enzalutimide but it didn't work so they switched him to Abiraterone in 2019 which has worked for a while but has now stopped being effective
- they tried another shot of RT to his spine to reduce the tumour pressing on his spinal cord (worth noting that palliative RT is not expected to reduce the PSA because it isn't treating the cancer)
- in July this year they tried Zometa to strengthen his bones but for some reason stopped after one infusion
- they were going to try Xofigo (radium 223) to reduce the bone tumours a bit but the SCC has meant this is not now appropriate
- he has continued with the Zoladex throughout this time
If that is the correct timeline, your relative has had advanced cancer since not long after his operation all those years ago but, because prostate cancer cells learn eventually to survive without testosterone, the hormone therapies that dad has had over the years have stopped working.
You are concerned about what other treatments could be tried but in fact, he stopped having treatments that would control his cancer in June this year - the Zometa, RT and Xofigo were about trying to reduce pain, prevent SCC and improve his quality of life not about treating the actual cancer. Now his cancer has progressed further, all they can do to achieve those objectives is try to get the pain relief right and, if possible, keep him mobile. I hope that the onco or GP has referred him to the palliative care team or local hospice? If not, get on to them witrhout delay to get this sorted - the hospice / palliative care team will be best placed to get the pain meds balanced as much as possible and arrange any equipment he needs for mobility - the palliative or community physios and occupational therapists should also be involved. Depending on his age, he may be entitled to money from the government to pay for any equipment or home care that might be needed in the future - the hospice team will usually have a social worker or support worker who can advise & help with form filling. They will also want to start having gentle conversations with your relative and you as a family about end stage - what would he like in terms of care, where would he like to be, that kind of thing. It is better (less scary or distressing for all of you) to have these conversations now rather than when he deteriorates.
I would expect that he will continue to have the Zoladex right up to the end - it may not be treating the cancer but will still be slowing it down.