Post primary treatment of recurrence is a gray area with no clear guidelines. The TOAD study found advantage to early ADT, but it is considered to be a weak study. My first MO recommended starting ADT at a PSA around 20, or radiographic evidence, whichever came first. My second MO basically had the same philosophy. He wasn't concerned about
the PSA value as much as he was concerned with PSA doubling time, mets visible on a scan, or physical symptoms.
My PSA doubling time took a big jump when it came back at 64, so I probably should have started ADT three months earlier. I'm not really concerned because my PSA dropped like a rock after starting ADT. But, time will tell.
Of course, different MOs have different views. Patient comfort with an increasing PSA factors into the decision. I suspect many patients are started on palliative ADT much earlier than necessary. The link below has a good discussion.https://ascopubs.org/doi/full/10.1200/edbk_200319