Clinical evaluation of a novel method for the measurement of prostate-specific antigen, AccuPSATM, as a predictor of 5-year biochemical recurrence-free survival after radical prostatectomy: results of a pilot study

Study Type Diagnostic (validating cohort) Level of Evidence 1b What's known on the subject? and What does the study add? Nadir Ultrasensitive PSA levels has some value for predicting BCR following RD. AccuPSA assays lower limit of PSA quantification of <0.01 pg/ml greatly enhances sensitivity and specificity of nadir PSA to predict BCR following RP. Our pilot study shows an AccuPSA of 3 pg/ml has a sensitory and specificity of 100% and 75% respectively for predicting 5 year BCR following RP. OBJECTIVES To conduct a proof of concept study to evaluate a novel digital single molecule immunoassay (AccuPSATM) that detects prostate-specific antigen (PSA) a thousandfold more sensitively than current PSA detection methods. To determine the ability of the AccuPSATM assay to predict 5-year biochemical recurrence (BCR)-free survival after radical prostatectomy (RP). PATIENTS AND METHODS A total of 31 frozen serum specimens were obtained from specimen logs maintained at New York University Langone Medical Center and the Johns Hopkins University School of Medicine on men who had undergone RP. Those men without evidence of BCR had a minimum of 5 years' PSA follow-up. In all cases, preoperative and pathological information were available, as was a serum specimen 36 months after RP, with a PSA level of <0.1 ng/mL measured by conventional PSA methods at the time of serum collection. Specimens were tested using the AccuPSATM method. A Cox proportional hazard model and KaplanMeier analysis were used to determine whether AccuPSATM predicted the risk of BCR. RESULTS Overall, 11/31 (35.5%) men developed BCR. Mean AccuPSATM nadir levels were significantly different (P < 0.001) between the non-BCR group (2.27 pg/mL) and the BCR group (46.99 pg/mL). Using a multivariate Cox proportional hazard model, AccuPSATM nadir level was a significant predictor of BCR-free survival (P < 0.01). KaplanMeier analysis of up to 5 years follow-up showed that 100% of men with AccuPSATM nadir values <3 pg/mL did not develop BCR, whereas 62.5% of men with values >3 pg/mL developed BCR (P= 0.00024). The sensitivity, specificity, positive predictive value and negative predictive value of the AccuPSATM method was 100%, 75%, 69% and 100%, respectively. CONCLUSIONS AccuPSATM assay predicts 5-year BCR- free survival after RP. Identifying a reliable predictor of BCR soon after RP has important implications for frequency of PSA testing, selection of candidates for adjuvant therapy, and reassuring a large subset of men that they are not at risk of recurrence. Larger studies are needed to validate these findings.