HALF-LIFE DETERMINATION OF SERUM-FREE PROSTATE-SPECIFIC ANTIGEN FOLLOWING RADICAL RETROPUBIC PROSTATECTOMY

Objectives, Prostate-specific antigen (PSA) continues to be the the mo st clinically useful tumor marker for prostate cancer. Recently, sever al molecular forms of PSA have been detected and characterized. These specific forms, including free PSA and PSA complexed to alpha(1)-antic hymotrypsin can be measured and their proportions determined. In doing so, the sensitivity of PSA as a tumor marker can be maintained while the specificity is improved. In order to maximize the clinical utility of free PSA, the half-life and elimination kinetics of free PSA from the serum were determined. Methods, Twenty-five patients, ages 43-74 y ears (mean 60 years) with biopsy proven, organ-confined adenocarcinoma of the prostate who underwent anatomic radical retropubic prostatecto my, were identified. For each patient, venous blood samples were obtai ned preoperatively, and at 60-minute intervals beginning hour after th e prostate was removed. The specimens were handled and stored in a con sistent fashion. Using the AxSYM(R) immunoassay analyzer (Abbott Diagn ostics, Abbott Park, IL), the serum free PSA values were determined an d plotted as a function of time for each patient. From the 25 individu al elimination curves that were generated, the half-life of serum free PSA was determined. Results. The mean half-life of serum free PSA was 110 minutes +/- 18.6 minutes (SD), Analysis of the individual and cum ulative elimination curves indicates that the elimination of free PSA from the serum following radical prostatectomy follows a biphasic patt ern. Conclusions, Unlike PSA, which has a half life of 2-3 days, the h alf-life of serum free PSA is 110 minutes (1.83 hours). This short hal f-life may have significant implications for the use of percentage of free PSA as a clinically useful tool in distinguishing patients with e arly, curable prostate cancer from men with benign prostatic hyperplas ia (BPH) only. Copyright 1996 by Elsevier Science Inc.