The prostate health index and the percentage of [-2]proPSA maintain their diagnostic performance when calculated with total and free PSA from different manufacturers

OBJECTIVES

To evaluate the diagnostic performance of the prostate health index (PHI) and of the percentage of [-2]proPSA (%[-2]proPSA) calculated with total and free PSA from non-Beckman Coulter manufacturers (Roche and Abbott), and compare it with the fully Beckman Coulter [-2]proPSA derivatives.

METHODS

In this study, 237 men (PSA: 2-10 μg/L) scheduled for prostate biopsy were enrolled. %[-2]proPSA and PHI were calculated with total and free PSA from three manufacturers. Beckman Coulter PSA and [-2]proPSA were performed on the Access 2 analyzer (Hybritech calibration). Roche PSA was performed on the cobas e411 and the Abbott PSA on the Architect i2000sr. Statistical analysis was performed, considering prostate cancer (PCa) as the outcome.

RESULTS

Univariate analysis showed that all indices were predictors of cancer, irrespective of the manufacturer (p<0.001). The AUC was similar for all manufacturers, both for %[-2]proPSA (Beckman Coulter: 0.756; Roche: 0.770; Abbott: 0.756) and PHI (Beckman Coulter: 0.776; Roche: 0.785; Abbott: 0.778). When considering the cutoffs that allowed 90% sensitivity, [-2]proPSA derivatives calculated with Roche and Abbott PSA had similar specificities and predictive values when compared to Beckman Coulter. The percentage of missed cancers (8-9%) was the same between manufacturers. The percentage of spared biopsies was significantly higher with Roche's PHI (21.0%) and Abbott's PHI (20.6%) than with Beckman Coulter's PHI (17.2%).

CONCLUSIONS

In the PSA range between 2 and 10 μg/L, [-2]proPSA derivatives maintain their diagnostic performance in PCa detection when calculated with PSA from Roche and Abbott. This can lead to a broader implementation of these indices in clinical laboratories worldwide.

Clinical interpretation of prostate-specific antigen values: Type of applied cut-off value exceeds methods bias as the major source of variation

BACKGROUND

Prostate-specific antigen is the biochemical gold standard for the (early) detection and monitoring of prostate cancer. Interpretation of prostate-specific antigen is both dependent on the method and cut-off. The aim of this study was to examine the effect of method-specific differences and cut-off values in a national external quality assessment scheme (EQAS).

METHODS

The Dutch EQAS for prostate-specific antigen comprised an annual distribution of 12 control materials. The results of two distributions were combined with the corresponding cut-off value. Differences between methods were quantified by simple linear regression based on the all laboratory trimmed mean. To assess the clinical consequence of method-specific differences and cut-off values, a clinical data-set of 1040 patients with an initial prostate-specific antigen measurement and concomitant conclusive prostate biopsy was retrospectively collected. Sensitivity and specificity for prostate cancer were calculated for all EQAS participants individually.

RESULTS

In the Netherlands, seven different prostate-specific antigen methods are used. Interestingly, 67% of these laboratories apply age-specific cut-off values. Methods showed a maximal relative difference of 26%, which were not reflected in the cut-off values. The largest differences were caused by the type of cut-off, for example in the Roche group the cut-off value differed maximal 217%. Clinically, a fixed prostate-specific antigen cut-off has a higher sensitivity than an age-specific cut-off (mean 89% range 86-93% versus 79% range 63-95%, respectively).

CONCLUSIONS

This study shows that the differences in cut-off values exceed the method-specific differences. These results emphasize the need for (inter)national harmonization/standardization programmes including cut-off values to allow for laboratory-independent clinical decision-making.

Discordant prostate specific antigen test results despite WHO assay standardization

Introduction:

Total PSA (tPSA) and free PSA (fPSA) are the most commonly used biomarkers for early detection of prostate cancer. Despite standardization efforts, many available PSA assays may still produce discordant results. In the present study, we compared four PSA assays calibrated to the WHO standards 96/670 and 96/668 for tPSA and fPSA, respectively.

Methods:

Within the scope of the Prostate Cancer Early Detection Study Based on a ‘‘Baseline’’ PSA Value in Young Men (PROBASE), we tested tPSA and fPSA in serum samples from 50 patients in the four different PROBASE sites using four WHO-calibrated assays from Roche (Elecsys, Cobas), Beckman-Coulter (Access-II) and Siemens (ADVIA Centaur). The comparison was performed using the Passing–Bablok regression method.

Results:

Compared to Access, the median tPSA levels for Centaur, Elecsys, and Cobas were +3%, +11%–20%, and +17%–23%, respectively, while for median fPSA levels the differences for Centaur, Elecsys, and Cobas were +49%, +29%–31%, and +22%, respectively.

Discussion:

Despite all investigated assays being WHO-calibrated, the Elecsys and Cobas tPSA assays produced considerably higher results than the Access and Centaur assays. Differences in fPSA-recovery between all investigated assays were even more pronounced. When applying the tPSA cutoff of 3.1 μg/L recommended for WHO-calibrated assays, the use of higher calibrated assays may lead to unnecessary prostate biopsies. Conversely, if the historical threshold of 4 μg/L is applied when using WHO-calibrated assays, it could lead to falsely omitted prostate biopsies.

Building bridges to the future of medicine: recommendations for boosting development of novel and companion diagnostics

Evaluating the prospects for ‘personalized healthcare’ has become topical at the 10-year anniversary of the first results from the Human Genome Project. The coincidence of this milestone with a period of global financial difficulty is unfortunate, but industry has signaled its willingness to invest in this new medical paradigm in order to address the problems of high drug candidate attrition as well as escalating healthcare and R&D costs. For diagnostics manufacturers, justifying the ever-growing costs of development without an appropriate framework to provide reasonable return on investment is extremely challenging. Regulators have made good progress in defining what will satisfy current regulatory mandates, but there is still far to go to create conditions that would stimulate investment. My personal perspective is that personalized healthcare represents a solution rather than a problem and herein I describe the bottlenecks slowing development of novel diagnostics from the perspective of a willing commercial stakeholder.

Glycans as Biomarkers: Status and Perspectives

Protein glycosylation is a ubiquitous and complex co- and post-translational modification leading to glycan formation, i.e. oligosaccharide chains covalently attached to peptide backbones. The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is widely recognized. Thus, glycans are considered as unique structures to diagnose, predict susceptibility to and monitor the progression of disease. In the »omics« era, the glycome, a glycan analogue of the proteome and genome, holds considerable promise as a source of new biomarkers. In the design of a strategy for biomarker discovery, new principles and platforms for the analysis of relatively small amounts of numerous glycoproteins are needed. Emerging glycomics technologies comprising different types of mass spectrometry and affinity-based arrays are next in line to deliver new analytical procedures in the field of biomarkers. Screening different types of glycomolecules, selection of differentially expressed components, their enrichment and purification or identification are the most challenging parts of experimental and clinical glycoproteomics. This requires large-scale technologies enabling high sensitivity, proper standardization and validation of the methods to be used. Further progress in the field of applied glycoscience requires an integrated systematic approach in order to explore properly all opportunities for disease diagnosis.