Absolute quantification methods for Prostate-Specific antigen by Isotope-Dilution mass spectrometry

Prostate-specific antigen (PSA) is a diagnostic marker for prostate cancer; however, because it is a macromolecular glycoprotein with complex and diverse isoforms, it is difficult to standardize clinical PSA detection results. To overcome this limitation, herein, naturally extracted PSA was characterized as free PSA (fPSA), and the PSA solution was successfully quantified by amino acid analysis coupled with isotope-dilution mass spectrometry (AAA-IDMS) and enzymatic hydrolysis-IDMS; the results could be traced to the International System of Units (SI) through absolutely quantified amino acids and peptides. After protein hydrolysis or digestion condition optimization, amino acids and signature peptides were detected by liquid chromatography-mass spectrometry with the multiple reaction monitoring mode. The mass concentrations of PSA obtained through AAA-IDMS and enzymatic hydrolysis-IDMS were (75.3 ± 1.5) µg/g (k = 2) and (74.7 ± 1.7) µg/g (k = 2), respectively. The PSA weighted average mass concentration was (75.0 ± 1.6) µg/g (k = 2). The consistency assessment between the two methods was successfully validated, ensuring absolute quantitative accuracy. This study lays the foundation for the development of high-order reference materials for the clinical detection of PSA, which can improve the accuracy, reliability, and consistency of clinical PSA test results.

Clinical usefulness of circulating tumor markers

Tumor markers are a heterogeneous group of substances released by cancer cells into bloodstream, but also expressed by healthy tissues. Thus, very small concentrations can be present in plasma and serum from healthy subjects. Cancer patients tend to show increased levels correlating with tumor bulk, but false positive results could be present in patients with benign conditions. The correct interpretation of TM results could be challenging and many factors should be considered, from pre-analytical conditions to patient concomitant diseases. In this line, the Clinical Chemistry and Laboratory Medicine journal has made important contributions though several publications promoting the adequate use of TM and therefore improving patient safety. TM measurement offers valuable information for cancer patient management in different clinical contexts, such as helping diagnosis, estimating prognosis, facilitating early detection of relapse and monitoring therapy response. Our review analyzes the clinical usefulness of tumor markers applied in most frequent epithelial tumors, based on recent evidence and guidelines.

Verification of Harmonization of Serum Total and Free Prostate-Specific Antigen (PSA) Measurements and Implications for Medical Decisions

BACKGROUND

Previous studies have shown that the harmonization of prostate-specific antigen (PSA) assays remained limited even after the introduction of WHO International Standards. This information needs updating for current measuring systems (MS) and reevaluation according to established analytical performance specifications (APS) and the characteristics of antibodies used.

METHODS

Total (tPSA) and free (fPSA) PSA were measured in 135 and 137 native serum samples, respectively, by Abbott Alinity i, Beckman Access Dxl, Roche Cobas e801, and Siemens Atellica IM MSs. Passing-Bablok regression and difference plots were used to compare results from each MS to the all-method median values. Agreement among methods was evaluated against APS for bias derived from biological variation of the 2 measurands.

RESULTS

The median interassay CV for tPSA MSs (11.5%; 25-75th percentiles, 9.2-13.4) fulfilled the minimum APS goal for intermethod bias (15.9%), while the interassay CV for fPSA did not [20.4% (25-75th percentiles, 18.4-22.7) vs goal 17.6%]. Considering the all-method median value of each sample as reference, all tPSA MSs exhibited a mean percentage bias within the minimum goal. On the other hand, Alinity (+21.3%) and Access (-24.2%) were out of the minimum bias goal for fPSA, the disagreement explained only in minimal part by the heterogeneity of employed antibodies.

CONCLUSIONS

The harmonization among tPSA MSs is acceptable only when minimum APS are applied and necessitates further improvement. The marked disagreement among fPSA MSs questions the use of fPSA as a second-level test for biopsy referral.

Prostate cancer screening: guidelines review and laboratory issues

Background Prostate-specific antigen (PSA) remains as the most used biomarker in the detection of early prostate cancer (PCa). Clinical practice guidelines (CPGs) are produced to facilitate incorporation of evidence into clinical practice. This is particularly useful when PCa screening remains controversial and guidelines diverge among different medical institutions, although opportunistic screening is not recommended. Methods We performed a systematic review of guidelines about PCa screening using PSA. Guidelines published since 2008 were included in this study. The most updated version of these CPGs was used for the evaluation. Results Twenty-two guidelines were selected for review. In 59% of these guidelines, recommendations were graded according to level of evidence (n = 13), but only 18% of the guidelines provided clear algorithms (n = 4). Each CPG was assessed using a checklist of laboratory issues, including pre-analytical, analytical, and post-analytical factors. We found that laboratory medicine specialists participate in 9% of the guidelines reviewed (n = 2) and laboratory issues were frequently omitted. We remarked that information concerning the consequences of World Health Organization (WHO) standard in PSA testing was considered by only two of 22 CPGs evaluated in this study. Conclusions We concluded that the quality of PCa early detection guidelines could be improved properly considering the laboratory issues in their development.

An overview of translational prostate cancer cohorts for prognostic and predictive studies

The aim of this review is to describe the characteristics of patient cohorts commonly used for translational biomarker research in prostate cancer and to outline the most prominent contemporary cohorts which serve as a source of prognostic and predictive biomarkers. A non-systematic review of the literature was performed to identify and summarise well-characterized translational prostate cancer cohorts that provide state-of-the-art characterization of (i) primary and (ii) metastatic and castration-resistant prostate cancer. The main advantages and features of these cohorts are a substantial number of patients, unique patient groups, comprehensive genetic characterisation of tumours using multi-omics/next-generation sequencing approaches, high-quality control standards and fully or partially open data for the research community. This overview includes the contemporary cohorts which serve as a rich source of new targets for prognostic and predictive biomarkers as well as a reference database for validation of known biomarkers, therefore representing the cohorts whose impact extends over the current state of biomarker research into the near future (5-10 years).

Simultaneous Detection of Dual Prostate Specific Antigens Using Surface-Enhanced Raman Scattering-Based Immunoassay for Accurate Diagnosis of Prostate Cancer

Accurate analysis of specific biomarkers in clinical serum is essential for early diagnosis and treatment of cancer. Here, a surface-enhanced Raman scattering (SERS)-based immunoassay, using magnetic beads and SERS nano tags, was developed for the determination of free to total (f/t) prostate specific antigen (PSA) ratio to improve the diagnostic performance of prostate cancer. To assess the clinical applicability of the proposed method, SERS-based assays for the simultaneous detection of dual PSA markers, free PSA (f-PSA) and complexed PSA (c-PSA), were performed for clinical samples in the gray zone between 4.0 and 10.0 ng/mL. Our assay results for f/t PSA ratio showed a good linear correlation with those measured using the electrochemiluminescence (ECL) system installed in the clinical laboratory of the University Hospital. In addition, the simultaneous assay provided better precision than parallel assays for the detection of f-PSA and c-PSA in 13 clinical serum samples. Therefore, our SERS-based assay for simultaneous detection of dual PSA markers in clinical fluids has strong potential for application in the accurate diagnosis of prostate cancer.

Molecular Form Differences Between Prostate-Specific Antigen (PSA) Standards Create Quantitative Discordances in PSA ELISA Measurements

The prostate-specific antigen (PSA) assays currently employed for the detection of prostate cancer (PCa) lack the specificity needed to differentiate PCa from benign prostatic hyperplasia and have high false positive rates. The PSA calibrants used to create calibration curves in these assays are typically purified from seminal plasma and contain many molecular forms (intact PSA and cleaved subforms). The purpose of this study was to determine if the composition of the PSA molecular forms found in these PSA standards contribute to the lack of PSA test reliability. To this end, seminal plasma purified PSA standards from different commercial sources were investigated by western blot (WB) and in multiple research grade PSA ELISAs. The WB results revealed that all of the PSA standards contained different mass concentrations of intact and cleaved molecular forms. Increased mass concentrations of intact PSA yielded higher immunoassay absorbance values, even between lots from the same manufacturer. Standardization of seminal plasma derived PSA calibrant molecular form mass concentrations and purification methods will assist in closing the gaps in PCa testing measurements that require the use of PSA values, such as the % free PSA and Prostate Health Index by increasing the accuracy of the calibration curves.

Guidance on patient consultation. Current evidence for prostate-specific antigen screening in healthy men and treatment options for men with proven localised prostate cancer

The main objective of this review is to summarise, for primary and secondary care doctors, the management options and current supporting evidence for clinically localised prostate cancer. We review all aspects of management including current guidelines on early cancer detection and the importance of informed consent on PSA-based screening and assess the most common treatment options and the evidence for managing patients with low-, medium-, and high-risk disease.

Serum concentrations of prostate-specific antigen measured using immune extraction, trypsin digestion, and tandem mass spectrometry quantification of LSEPAELTDAVK peptide

CONTEXT

Prostate-specific antigen (PSA) is a 34-kDa glycoprotein with chymotrypsin-like enzyme activity that circulates both in free forms and complexed to various enzyme inhibitors including antichymotrypsin and α2-macroglobulin. Prostate-specific antigen bound to α2-macroglobulin is not detected by commercial PSA immunoassays.

OBJECTIVE

To develop a mass spectrometry assay that detects the same forms of PSA as the immunoassays, which could serve as a reference for harmonizing PSA immunoassays.

DESIGN

Prostate-specific antigen was immune extracted from serum, trypsin was digested, and the LSEPAELTDAVK peptide was quantitated on an API 5000 spectrometer. Calibrators were made by adding 10% free and 90% antichymotrypsin-bound PSA to female sera. The assay was standardized to the World Health Organization 96/670 reference standard. Validation of clinical utility and comparisons with 2 immunoassays (Roche cobas and Beckman Access) were performed using frozen sera aliquots from 100 men undergoing prostate biopsy (50 negative, 50 with cancer) and 5 serial samples collected over time from 5 men with advanced prostate cancer.

RESULTS

The antibody extraction efficiency was greater than 99%. The assay has an analytic range from 1.2 to 76 ng/mL, with precision ranging from 8.6% at 1.5 ng/mL to 5.4% at 27 ng/mL. The mass spectrometry assay correlated well with 2 immunoassays. All 3 assays showed statistically equivalent separation of prostate cancer from benign disease using receiver operating characteristic curve analysis.

CONCLUSIONS

This mass spectrometry assay can reliably measure PSA concentrations in human serum and could serve as a reference standard for harmonizing PSA immunoassays.

Bone turnover markers in serum and urine as diagnostic, prognostic and monitoring biomarkers of bone metastasis

Bone metastases are characterized by increased osteoblastic and/or osteolytic processes depending on the tumor type. The altogether destructive effect of metastasis formation promoted by increased metabolic activity raises the release of components from the osseous metabolism into the blood stream. These components are either enzymes directly involved in the alteration processes, metabolites/proteins that develop during this or bone matrix proteins released during this. These biomarkers are categorized in relation to their involvement in the bone formation or resorption as bone formation and resorption markers. Based on a PubMed literature search, a critical appraisal of the various biomarkers for diagnostic, prognostic, and monitoring purposes is given for patients with skeletal metastases caused by breast, prostate, lung, or renal cell carcinomas.

[Prostate biopsy. Update for indication, procedure, and future developments]

Transrectal ultrasound-guided prostate biopsy is considered the gold standard in the primary investigation of a suspicious prostate-related finding. The procedure can be carried out with ten probes or more on the lateral side of the prostate, after administering antibiotic prophylaxis and applying local anesthesia. The indication for a biopsy depends on the results of the digitorectal examination, on the serum prostate-specific antigen level, on the individual patient's wish and on his comorbidities. Whether multiparametric imaging should be used before or during the course of a primary or repeated biopsy in order to identify suspicious prostate lesions is the subject of current investigations. Extended biopsy protocols require further clinical investigations before they can become the new standard in the diagnostic work-up. This review delivers an update on the indication for, and technique of, prostate biopsies.

Mass spectrometry measurements of prostate-specific antigen (PSA) peptides derived from immune-extracted PSA provide a potential strategy for harmonizing immunoassay differences

OBJECTIVES

Harmonization of prostate-specific antigen (PSA) immunoassays is important for good patient care. The specificity of the antibodies used to detect circulating PSA could cause differences in the PSA measurements.

METHODS

We used mass spectrometry (MS) to quantitate the concentration of five peptides cleaved from trypsin digestion of PSA and compared these measurements with six automated immunoassays. Linear regression and a mixed-effects model were used to analyze the results.

RESULTS

PSA measurements from the immunoassays and the five MS peptide assays were highly correlated (R(2) > 0.99), but the recovery of the World Health Organization standard and the regression slopes differed across assays. The same relative patterns of immunoassay differences were seen in comparing their results with each of the five MS peptide measurements from different parts of the circulating PSA molecules.

CONCLUSIONS

Mass spectrometry quantitation of peptides derived from trypsin digestion of immune-extracted PSA could be used to harmonize PSA immunoassays.

EAU guidelines on prostate cancer. part 1: screening, diagnosis, and local treatment with curative intent-update 2013

CONTEXT

The most recent summary of the European Association of Urology (EAU) guidelines on prostate cancer (PCa) was published in 2011.

OBJECTIVE

To present a summary of the 2013 version of the EAU guidelines on screening, diagnosis, and local treatment with curative intent of clinically organ-confined PCa.

EVIDENCE ACQUISITION

A literature review of the new data emerging from 2011 to 2013 has been performed by the EAU PCa guideline group. The guidelines have been updated, and levels of evidence and grades of recommendation have been added to the text based on a systematic review of the literature, which included a search of online databases and bibliographic reviews.

EVIDENCE SYNTHESIS

A full version of the guidelines is available at the EAU office or online (www.uroweb.org). Current evidence is insufficient to warrant widespread population-based screening by prostate-specific antigen (PSA) for PCa. Systematic prostate biopsies under ultrasound guidance and local anesthesia are the preferred diagnostic method. Active surveillance represents a viable option in men with low-risk PCa and a long life expectancy. A biopsy progression indicates the need for active intervention, whereas the role of PSA doubling time is controversial. In men with locally advanced PCa for whom local therapy is not mandatory, watchful waiting (WW) is a treatment alternative to androgen-deprivation therapy (ADT), with equivalent oncologic efficacy. Active treatment is recommended mostly for patients with localized disease and a long life expectancy, with radical prostatectomy (RP) shown to be superior to WW in prospective randomized trials. Nerve-sparing RP is the approach of choice in organ-confined disease, while neoadjuvant ADT provides no improvement in outcome variables. Radiation therapy should be performed with ≥ 74 Gy in low-risk PCa and 78 Gy in intermediate- or high-risk PCa. For locally advanced disease, adjuvant ADT for 3 yr results in superior rates for disease-specific and overall survival and is the treatment of choice. Follow-up after local therapy is largely based on PSA and a disease-specific history, with imaging indicated only when symptoms occur.

CONCLUSIONS

Knowledge in the field of PCa is rapidly changing. These EAU guidelines on PCa summarize the most recent findings and put them into clinical practice.

PATIENT SUMMARY

A summary is presented of the 2013 EAU guidelines on screening, diagnosis, and local treatment with curative intent of clinically organ-confined prostate cancer (PCa). Screening continues to be done on an individual basis, in consultation with a physician. Diagnosis is by prostate biopsy. Active surveillance is an option in low-risk PCa and watchful waiting is an alternative to androgen-deprivation therapy in locally advanced PCa not requiring immediate local treatment. Radical prostatectomy is the only surgical option. Radiation therapy can be external or delivered by way of prostate implants. Treatment follow-up is based on the PSA level.

Variability of assay methods for total and free PSA after WHO standardization

The variability of total PSA (tPSA) and free PSA (fPSA) results among commercial assays has been suggested to be decreased by calibration to World Health Organization (WHO) reference materials. To characterize the current situation, it is necessary to know its impact in the critical cutoffs used in clinical practice. In the present study, we tested 167 samples with tPSA concentrations of 0 to 20 μg/L using seven PSA and six fPSA commercial assays, including Access, ARCHITECT i2000, ADVIA Centaur XP, IMMULITE 2000, Elecsys, and Lumipulse G1200, in which we only measured tPSA. tPSA and fPSA were measured in Access using the Hybritech and WHO calibrators. Passing-Bablok analysis was performed for PSA, and percentage of fPSA with the Hybritech-calibrated access comparison assay. For tPSA, relative differences were more than 10 % at 0.2 μg/L for ARCHITECT i2000, and at a critical concentration of 3, 4, and 10 μg/L, the relative difference was exceeded by ADVIA Centaur XP and WHO-calibrated Access. For percent fPSA, at a critical concentration of 10 %, the 10 % relative difference limit was exceeded by IMMULITE 2000 assay. At a critical concentration of 20 and 25 %, ADVIA Centaur XP, ARCHITECT i2000, and IMMULITE 2000 assays exceeded the 10 % relative difference limit. We have shown significant discordances between assays included in this study despite advances in standardization conducted in the last years. Further harmonization efforts are required in order to obtain a complete clinical concordance.

[EAU guidelines on prostate cancer. Part I: screening, diagnosis, and treatment of clinically localised disease]

OBJECTIVE

Our aim was to present a summary of the 2010 version of the European Association of Urology (EAU) guidelines on the screening, diagnosis, and treatment of clinically localised cancer of the prostate (PCa).

METHODS

The working panel performed a literature review of the new data emerging from 2007 to 2010. The guidelines were updated, and level of evidence and grade of recommendation were added to the text based on a systematic review of the literature, which included a search of online databases and bibliographic reviews.

RESULTS

A full version is available at the EAU office or Web site (www.uroweb.org). Current evidence is insufficient to warrant widespread population-based screening by prostate-specific antigen (PSA) for PCa. A systematic prostate biopsy under ultrasound guidance and local anaesthesia is the preferred diagnostic method. Active surveillance represents a viable option in men with low-risk PCa and a long life expectancy. PSA doubling time in < 3 yr or a biopsy progression indicates the need for active intervention. In men with locally advanced PCa in whom local therapy is not mandatory, watchful waiting (WW) is a treatment alternative to androgen-deprivation therapy (ADT) with equivalent oncologic efficacy. Active treatment is mostly recommended for patients with localised disease and a long life expectancy with radical prostatectomy (RP) shown to be superior to WW in a prospective randomised trial. Nerve-sparing RP represents the approach of choice in organ-confined disease; neoadjuvant androgen deprivation demonstrates no improvement of outcome variables. Radiation therapy should be performed with at least 74Gy and 78Gy in low-risk and intermediate/high-risk PCa, respectively. For locally advanced disease, adjuvant ADT for 3 yr results in superior disease-specific and overall survival rates and represents the treatment of choice. Follow-up after local therapy is largely based on PSA, and a disease-specific history with imaging is indicated only when symptoms occur.

CONCLUSIONS

The knowledge in the field of PCa is rapidly changing. These EAU guidelines on PCa summarise the most recent findings and put them into clinical practice.

EAU guidelines on prostate cancer. Part 1: screening, diagnosis, and treatment of clinically localised disease

OBJECTIVE

Our aim was to present a summary of the 2010 version of the European Association of Urology (EAU) guidelines on the screening, diagnosis, and treatment of clinically localised cancer of the prostate (PCa).

METHODS

The working panel performed a literature review of the new data emerging from 2007 to 2010. The guidelines were updated, and level of evidence and grade of recommendation were added to the text based on a systematic review of the literature, which included a search of online databases and bibliographic reviews.

RESULTS

A full version is available at the EAU office or Web site (www.uroweb.org). Current evidence is insufficient to warrant widespread population-based screening by prostate-specific antigen (PSA) for PCa. A systematic prostate biopsy under ultrasound guidance and local anaesthesia is the preferred diagnostic method. Active surveillance represents a viable option in men with low-risk PCa and a long life expectancy. PSA doubling time in <3 yr or a biopsy progression indicates the need for active intervention. In men with locally advanced PCa in whom local therapy is not mandatory, watchful waiting (WW) is a treatment alternative to androgen-deprivation therapy (ADT) with equivalent oncologic efficacy. Active treatment is mostly recommended for patients with localised disease and a long life expectancy with radical prostatectomy (RP) shown to be superior to WW in a prospective randomised trial. Nerve-sparing RP represents the approach of choice in organ-confined disease; neoadjuvant androgen deprivation demonstrates no improvement of outcome variables. Radiation therapy should be performed with at least 74 Gy and 78 Gy in low-risk and intermediate/high-risk PCa, respectively. For locally advanced disease, adjuvant ADT for 3 yr results in superior disease-specific and overall survival rates and represents the treatment of choice. Follow-up after local therapy is largely based on PSA, and a disease-specific history with imaging is indicated only when symptoms occur.

CONCLUSIONS

The knowledge in the field of PCa is rapidly changing. These EAU guidelines on PCa summarise the most recent findings and put them into clinical practice.