Background: In this paper we study the Free/Total PSA kinetics in patients with clinically localized prostate cancer undergoing radical prostatectomy.
Methods: Serum PSA, Free PSA and Free/Total Ratio were determined preoperatively, at the time of prostate removal (0 time) and then at 3, 6, 12, 24, 48, 72 and 168 h, from 9 patients with clinically localized prostate cancer who underwent radical retropubic prostatectomy. The elimination rates and half-lives of Total, Free PSA and F/T Ratio were studied applying one and two compartment models for pharmacokinetic analysis.
Results: Surgical manipulations of the prostate caused a mean 2.16-fold increase of PSA, 12-fold increase of free PSA and 4.2-fold increase of F/T PSA ratio. Removal of the prostate caused a rapid biphasic, biexponential elimination of Free PSA with a mean half-life of 0.8 h for the alpha (a) phase and 32.6 h for the beta (b) phase. PSA was eliminated following a rapid exponential (a) phase with a half-life of 1.15 h and a non-exponential (b) phase with a half-life of 71.96 h. Free/Total PSA followed a biphasic kinetic, with an initial exponential elimination phase and a mean half-life of 2.6 h and a second non-exponential increase phase with a doubling time of 130.8 h. Free/Total PSA reached its nadir very soon, at the first postoperative 24 h.
Conclusions: Free/Total PSA kinetic after radical prostatectomy reflects the differences of Free and Total PSA elimination kinetics. Free/Total Ratio follows a biphasic kinetic, with an initial rapid exponential elimination phase, which is affected mainly by the rapid exponential (a) phase of Free PSA elimination and a second slow increase, which is affected mainly by the terminal non-exponential (b) phase of PSA elimination.