Ultrasensitive serum prostate specific antigen nadir accurately predicts the risk of early relapse after radical prostatectomy

Purpose: Ultrasensitive prostate specific antigen (PSA) assays allow a lower limit of detection (less than 0.01 ng/ml) than standard PSA assays. In this study we examined the ability of ultrasensitive PSA nadir to predict relapse after radical prostatectomy (RP). Materials and Methods: A total of 906 men treated with RP were followed with PSA measurements at 3, 6 and 12 months, and yearly thereafter. Of the 906 men 545 (60%) with a PSA nadir of less than 0.01 ng/ml or at least 3 followup ultrasensitive PSA measurements underwent analysis and stratification by PSA nadir. Biochemical relapse was defined as 2 consecutive increasing post-nadir PSA measurements of 0.1 ng/ml or greater. The ability of ultrasensitive PSA nadir to predict relapse was assessed by univariate and multivariate analysis. Results: At a mean followup of 3.1 years 54 of 545 men (9.9%) experienced biochemical relapse with a mean time to relapse of 25.2 months. Relapse rates in men with a PSA nadir of less than 0.01 (423), 0.01 (75), 0.02 (19) and 0.04 or greater ng/ml (28) were 4%, 12%, 16% and 89%, respectively. Men with a nadir of less than 0.01 ng/ml had a significantly lower relapse rate than men with a nadir of 0.01 (p <0.01), 0.02 (p <0.025) or 0.04 or greater ng/ml (p <0.01). Multivariate logistic regression analysis showed that a nadir of 0.01 (p <0.05), 0.02 (p <0.05) and 0.04 or greater ng/ml (p <0.01) independently predicted an increased risk of biochemical relapse compared to a nadir of less than 0.01 ng/ml. Conclusions: Ultrasensitive PSA nadir accurately predicts the risk of early biochemical relapse following RP. Men who achieve a nadir of less than 0.01 ng/ml have a low likelihood of early relapse. Higher nadir points may identify candidates for early adjuvant or salvage therapies.