BACKGROUND Measurement of prostate specific antigen (PSA) in prostate cancer patients following radical prostatectomy (RP) has been limited by the sensitivity of available assays. Because radical prostatectomy removes the tissue responsible for PSA production, post-surgical PSA is typically undetectable with current assay methods. However, evidence suggests that more sensitive determination of PSA status following RP could improve assessment of patient prognosis, response to treatment, and better target secondary therapy to those who may benefit most. We report the development and validation of an investigational digital immunoassay with two logs greater sensitivity than today’s ultrasensitive third-generation PSA assays. METHODS Reagents were developed for a paramagnetic bead-based ELISA for use with high-density arrays of femtoliter-volume wells. Anti-PSA capture-beads with immunocomplexes and associated enzyme labels were singulated within the wells of the arrays and interrogated for the presence of enzymatic product. Analytical performance of the assay was characterized, its accuracy compared with a commercially available test, and longitudinal serum samples from a pilot study of 33 RP patients were analyzed. RESULTS The assay exhibited a functional sensitivity (20% inter-assay CV) of less than 0.00005 ng/mL (0.05 pg/mL), total imprecision of less than 10% from 1 to 50 pg/mL, and excellent agreement with the comparator method. All RP samples were well within the assay measurement capability. PSA values following surgery were examined in the context of five-year biochemical cancer recurrence. CONCLUSION The assay demonstrated a robust two-log advance in measurement sensitivity relative to current ultrasensitive assays, and the analytical performance for accurate assessment of PSA status after RP.
Aims of the study: Retrospective studies investigating the use of percent free free-PSA for early detection of prostate cancer were limited for various reasons: by their use of long-term stored sera, poor mix of non-cancer to cancer cases and the use of only men with PSA values between 4.0 and 10.0 ngamL. This prospective study investigates the clinical utility of percent free-PSA and complexed-PSA for early detection of prostate cancer in 219 consecutive men presenting for prostate biopsy. Methods: Of 246 consecutive men who underwent ultrasound guided sextant biopsy of the prostate for PSA elevation andaor suspicious digital rectal exam, 219 men had serum total PSA levels between 2.0 and 20.0 ngamL and were included in this study. Serum total, free and complexed (PSA±ACT) were measured (Hybritech Inc.). Results: Pathologic examinations demonstrated that 72% and 28% of the biopsies were non-cancer and cancer respectively. The mean percent free-PSA was statistically different between the groups (cancer 14% AE 6.4 and non-cancer 18 AE 9%, P`0.001) and improved cancer detection. PSA±ACT provided only modest improvement in cancer detection over that of total PSA. Among this cohort of men, the optimal total PSA re¯ex range for percent free-PSA was 3.0 ± 7.0 ngamL (38% speci®city) with a percent free free-PSA cut-off of 20% (95% sensitivity) yet only affected 56% of the cases. Conclusions: PSA±ACT added very little additional value to the clinical utility of total PSA for early detection. Percent free free-PSA performed well for all re¯ex ranges. A sensitivity and speci®city of 95% and 20% respectively were obtained using a single cut-off of 25% for percent free-PSA for the group of men with total PSA values between 4.0 and 10.0 and correlated well with recently reported prospective analyses.
The application of SELDI-TOF to a series of Dunning rat prostate cancer cell lines illustrated apparent changes in protein profiles among the three cell lines with known differences in metastatic biologic activity. SELDI-TOF identified four reproducible changes in protein expression in the AT1 and MLL metastatic cell sublines. Three of the expression changes were manifested as decreases, but one protein (17 kDa) was over-expressed in the AT1 and MLL cell lines. Emphasis will be placed on the isolation, purification, and characterization of the 17 kDa over-expressed protein and its potential role in PCa metastasis.
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 3–6 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 Kaplan–Meier 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). Kaplan–Meier 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.
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