It didn't come back without any warning. My PSA was undetectable for a year or so after surgery, then started creeping up very slowly using the ultra sensitive PSA. But it was too low to do anything about and there was no way to determine where the PSA was coming from ("low and slow" as my doctor put it). It reached 0.2 after 15 years, and the PSMA became available (I'm a UCSF patient and they co developed the PSMA). It was detected in the prostate bed so they were able to target the radiation.