Quality assessment for prostate-specific antigen (PSA) in relation to ERSPC: report of the PSA Committee

Toward metrological traceability in the determination of prostate-specific antigen (PSA): calibrating Beckman Coulter Hybritech Access PSA assays to WHO standards compared with the traditional Hybritech standards

BACKGROUND

The metrological traceability of prostate-specific antigen (PSA) assay calibration to WHO standards is desirable to potentially improve the comparability between PSA assays. A method comparison was performed between the traditionally standardized Beckman Coulter Hybritech Access PSA and free PSA (fPSA) assays and a new alternate calibration of assays aligned to the WHO standards 96/670 and 96/668, respectively.

METHODS

Sera from 641 men with and without prostate cancer, various control materials and mixtures of different proportions of the WHO standards were measured with both assay calibrations.

RESULTS

Excellent comparability between the corresponding assay calibrations was observed, with correlation coefficients of at least 0.996. The Passing-Bablok slopes were 0.747 for total PSA (tPSA), 0.776 for fPSA and 1.02 for the percentage ratio of fPSA to tPSA (%fPSA), while the corresponding percentages of the new WHO-aligned assay results related to the traditional assays were 76.2%, 77% and 102.2%. Receiver operating characteristics revealed no differences between the two PSA assay calibrations.

CONCLUSIONS

The WHO calibration yields results approximately 25% lower for tPSA and fPSA values when compared with the conventional Hybritech calibration. Using the WHO-aligned PSA assay, a tPSA cut-off of 3 microg/L should be considered in clinical practice, while %fPSA cut-offs could be retained.

Effect of thrombin tube on PSA determination, a clue for false negative in screening for prostate cancer

Prostate cancer is an important male carcinoma. Laboratory screening for tumor marker is the routine preventive strategy for control of this cancer. For screening, prostate specific antigen (PSA) has been proposed as a marker in the serum. In this article, the author assesses the effect of new blood collection tube, thrombin tube, on the analysis of the PSA by bioinformatics technique. Using GoFigure server, the molecular functions of thrombin, PSA and thrombin-PSA were predicted. A significant change of molecular function due to the interaction between thrombin and PSA can be found. Increased of coagulation due to the synergistic clot activation can be expected. If this occurs, the false negative can be expected and it can bring the underdiagnosis of early prostate cancer. Therefore, the recommendation for usage of thrombin tube for PSA test should be modified from general usage. Shortening of the period between blood collection and sample analysis than general case must be done.

The value of different screening tests in predicting prostate biopsy outcome in screening for prostate cancer data from a multicenter study (ERSPC)

BACKGROUND

Although serum PSA testing is widely used as a screening test for prostate cancer (PC), it is known that it is not specific for PC. The study described here focuses on the value of screening tests next to PSA in identifying men with an elevated risk of having PC and the differences between three centers of the European Randomised study of Screening for Prostate Cancer (ERSPC).

METHODS

The study population consists of 2,483 men with a PSA > or =4.0 ng/ml, all biopsied. We assessed data on age, serum PSA level at initial and repeat screening, prostate volume, number of positive DRE and TRUS findings, number of previous negative biopsies, and PPV of the three centers and overall. Using logistic regression analysis, predictors for biopsy outcome at repeat screening in men with a PSA value > or =4.0 ng/ml were determined on the complete dataset and per center.

RESULTS

In 2,483 men biopsied, 665 cancers were detected (PPV = 26.8%). Data show that all predictors except prostate volume loose their predictive value in men previously biopsied. In men not previously biopsied, the predictive value of DRE and TRUS vary considerably among the three centers.

CONCLUSIONS

Looking at the differences in the predictive value of screening tests in three "comparable" centers, generasibility is not as straightforward as it seems. Using a nomogram for predictive purposes developed elsewhere will require a thorough knowledge of the patient population of which it is derived, and one should interpret its results with a critical mind.

Randomized, double-blind, placebo-controlled crossover study in men with prostate cancer and rising PSA: effectiveness of a dietary supplement

OBJECTIVES

Epidemiological studies have shown significant relationships between the use of dietary components and prostate cancer incidence and mortality. Large studies of primary prevention, which confirm these findings, are desirable but costly and difficult to design. The present tertiary prevention study reports on the effect of a dietary supplement in comparison with placebo on the rate of increase of prostate-specific antigen (PSA).

METHODS

49 patients with a history of prostate cancer and rising PSA levels after radical prostatectomy (n = 34) or radiotherapy (n = 15) participated in a randomised, double-blind, placebo-controlled crossover study of a dietary supplement. Ethical approval of the protocol was obtained. Treatment periods of 10 weeks were separated by a 4-week washout period. The supplement consisted of soy, isoflavones, lycopene, silymarin and antioxidants as main ingredients. Changes in the rate of increase of PSA (PSA slope and doubling time) were the primary parameters of efficacy. Analyses according to intention to treat (ITT) and per protocol (PP) were carried out.

RESULTS

Baseline parameters did not differ between randomised groups. Five participants were lost to follow-up, however 46 could be evaluated in an ITT analysis. PP analysis could be performed in 42 men with at least 5 PSA measurements. Per protocol analysis showed a significant decrease in PSA slope (p = 0.030) and (2)log PSA slope (p = 0.041). This translates into a 2.6 fold increase in the PSA doubling time from 445 to 1150 days for the supplement and placebo periods. No treatment-based changes in safety parameters were observed during the study.

CONCLUSIONS

The soy-based dietary supplement utilised in this study was shown to delay PSA progression after potentially curative treatment in a significant fashion. More extensive studies of the supplement may be indicated.