Objectives. To investigate whether the second-order kinetics model of prostate-specific antigen (PSA) increase would be more appropriate in some cases than the traditionally assumed first-order model. PSA levels are used to detect tumor recurrence after radical prostatectomy, and the rate of PSA increase is used to predict patients' prognosis. Methods. Sequential PSA values from 147 patients showing detectable PSA after radical prostatectomy were analyzed by nonlinear regression analysis. The best-fitting model was chosen using the lowest sum of squares residual error. Results. Of the 147 cases, 90 (61.2%) followed the first-order kinetics, and 57 (38.8%) were better described by second-order kinetics. The order of PSA increase correlated with the Gleason score of the tumor in the radical prostatectomy specimens. The first-order kinetics were associated with tumors with Gleason scores of 5 to 6, 7, and 9, and the second-order kinetics were associated with tumors with a Gleason score of 8 (P <0.01). Our data did not show a correlation between the order of PSA increase and the clinical prognosis. Conclusions. The presence of a group of tumors in which the increase in PSA follows second-order kinetics is significant. Such an increase may be associated with an autocatalytic mechanism assisting tumor growth. The existence of such a mechanism requires additional investigation.
ASJC Scopus subject areas