This plot from Safriadi (2022) compares the mean values of PSA nadir versus Testosterone Nadir comparing Non-Castrate Resistant PC (Non-CRPC) to Castrate-Resistant PC (CRPC) men.
For Non-CRPC men, the range of T-nadir was 2.5-49 ng/dL (mean = 21) and range for PSA nadir was 0.02-9 ng/mL (mean=2).
For CRPC men, the range of T-nadir was 4-49 ng/dL (mean=22) and range for PSA nadir was 0.1-49 ng/mL (mean=14).
I interpolated the two points down to (0,0), which seems reasonable to do.
The takeaway is that Non-CRPC men can achieve a much lower PSA nadir than CRPC men, for the same level of testosterone nadir. This makes sense, because CRPC men are less responsive to ADT, by definition.
PSA Dropped but Testosterone level unchanged 
