Well, I too, am deeply sorry to hear of this most recent development for you, and as always, I want to underscore that I am no doctor, so nothing I say here should be taken as 'gospel' or as a medical recommendation of any kind, but I know that if this were me, I would run (not walk) for second opinions on all of it, including a PSMA-PET scan if you've not had one yet.

If you underwent previous proton treatments, then presumably, you've had a biopsy long ago, and if so, wasn't there a Gleason score or Decipher test done at that time? I guess what I'm saying in summary is, that these many 'conclusions' that these various folks including Mayo have apparently given you (i.e., that your rectal pain was not from hemorrhoids, that its prostate cancer and an "aggressive" form of it at-that, and that none of it "raises your PSA"), should all be closely scrutinized and evaluated elsewhere. But that's just my 2-cents.

I'll hope that much (if not all!) of it, proves to be off-base, but either way, I wish you the very best. These are not easy episodes in our lives to deal with.