Discrimination of benign from malignant prostatic disease by selective measurements of single chain, intact free prostate specific antigen

Advancements in Biomarkers of Prostate Cancer: A Review

Prostate cancer (PCa) is one of the most prevalent and deadly cancers among men, particularly affecting men of African descent and contributing significantly to cancer-related morbidity and mortality worldwide. The disease varies widely, from slow-developing forms to highly aggressive or potentially fatal variants. Accurate risk stratification is crucial for making therapeutic decisions and designing adequate clinical trials. This review assesses a broad spectrum of diagnostic and prognostic biomarkers, many of which are incorporated into clinical guidelines, including the Prostate Health Index (PHI), 4Kscore, STHLM3, PCA3, SelectMDx, ExoDx Prostate Intelliscore (EPI), and MiPS. It also highlights emerging biomarkers with preclinical support, such as urinary non-coding RNAs and DNA methylation patterns. Additionally, the review explores the role of tumor-associated microbiota in PCa, offering new insights into its potential contributions to disease understanding. By examining the latest advancements in PCa biomarkers, this review enhances understanding their roles in disease management.

Molecular Biomarkers in the Clinical Management of Prostate Cancer

Prostate cancer, one of the most common noncutaneous malignancies in men, is a heterogeneous disease with variable clinical outcome. Although the majority of patients harbor indolent tumors that are essentially cured by local therapy, subsets of patients present with aggressive disease or recur/progress after primary treatment. With this in mind, modern clinical approaches to prostate cancer emphasize the need to reduce overdiagnosis and overtreatment via personalized medicine. Advances in our understanding of prostate cancer pathogenesis, coupled with recent technologic innovations, have facilitated the development and validation of numerous molecular biomarkers, representing a range of macromolecules assayed from a variety of patient sample types, to help guide the clinical management of prostate cancer, including early detection, diagnosis, prognostication, and targeted therapeutic selection. Herein, we review the current state of the art regarding prostate cancer molecular biomarkers, emphasizing those with demonstrated utility in clinical practice.

Prostate-specific antigen and other serum and urine markers in prostate cancer

Prostate-specific antigen (PSA) is one of the most widely used tumor markers, and strongly correlates with the risk of harboring from prostate cancer (PCa). This risk is visible already several years in advance but PSA has severe limitations for PCa detection with its low specificity and low negative predictive value. There is an urgent need for new biomarkers especially to detect clinically significant and aggressive PCa. From all PSA-based markers, the FDA-approved Prostate Health Index (phi) shows improved specificity over percent free and total PSA. Other serum kallikreins or sarcosine in serum or urine show more diverging data. In urine, the FDA-approved prostate cancer gene 3 (PCA3) has also proven its utility in the detection and management of early PCa. However, some aspects on its correlation with aggressiveness and the low sensitivity at very high values have to be re-examined. The detection of a fusion of the androgen regulated TMPRSS2 gene with the ERG oncogene (from the ETS family), which acts as transcription factor gene, in tissue of ~50% of all PCa patients was one milestone in PCa research. When combining the urinary assays for TMPRSS2:ERG and PCA3, an improved accuracy for PCa detection is visible. PCA3 and phi as the best available PCa biomarkers show an equal performance in direct comparisons.

Emerging PSA-based tests to improve screening

This article updates advances in prostate cancer screening based on prostate-specific antigen, its derivatives, and human kallikrein markers. Many men are diagnosed with indolent disease not requiring treatment. Although there is evidence of a survival benefit from screening, the numbers needed to screen and treat remain high. There is risk of exposing men to the side effects of treatment for nonthreatening disease. A screening test is needed with sufficiently good performance characteristics to detect disease at an early stage so treatment may be offered with curative intent, while reducing the number of negative or unnecessary biopsies.

Can one blood draw replace transrectal ultrasonography-estimated prostate volume to predict prostate cancer risk?

OBJECTIVE

To explore whether a panel of kallikrein markers in blood: total, free and intact prostate-specific antigen (PSA) and kallikrein-related peptidase 2, could be used as a non-invasive alternative for predicting prostate cancer on biopsy in a screening setting.

SUBJECTS AND METHODS

The study cohort comprised previously unscreened men who underwent sextant biopsy owing to elevated PSA (≥3 ng/mL) in two different centres of the European Randomized Study of Screening for Prostate Cancer, Rotterdam (n = 2914) and Göteborg (n = 740). A statistical model, based on kallikrein markers, was compared with one based on established clinical factors for the prediction of biopsy outcome.

RESULTS

The clinical tests were found to be no better than blood markers, with an area under the curve in favour of the blood measurements of 0.766 vs. 0.763 in Rotterdam and 0.809 vs. 0.774 in Göteborg. Adding digital rectal examination (DRE) or DRE plus transrectal ultrasonography (TRUS) volume to the markers improved discrimination, although the increases were small. Results were similar for predicting high-grade cancer. There was a strong correlation between the blood measurements and TRUS-estimated prostate volume (Spearman's correlation 0.60 in Rotterdam and 0.57 in Göteborg).

CONCLUSIONS

In previously unscreened men, each with indication for biopsy, a statistical model based on kallikrein levels was similar to a clinical model in predicting prostate cancer in a screening setting, outside the day-to-day clinical practice. Whether a clinical approach can be replaced by laboratory analyses or used in combination with decision models (nomograms) is a clinical judgment that may vary from clinician to clinician depending on how they weigh the different advantages and disadvantages (harms, costs, time, invasiveness) of both approaches.

Multicenter evaluation of [-2]proprostate-specific antigen and the prostate health index for detecting prostate cancer

BACKGROUND

Total prostate-specific antigen (tPSA) is flawed for prostate cancer (PCa) detection. [-2]proprostate-specific antigen (p2PSA), a molecular isoform of free PSA (fPSA), shows higher specificity compared with tPSA or percentage of free PSA (%fPSA). The prostate health index (Phi), a measure based on p2PSA and calculated as p2PSA/fPSA × √tPSA, was evaluated in a multicenter study for detecting PCa.

METHODS

A total of 1362 patients from 4 different study sites who had tPSA values of 1.6-8.0 μg/L (668 patients with PCa, 694 without PCa) underwent ≥10 core biopsies. Serum concentrations of tPSA, fPSA (both calibrated against a WHO reference material), and p2PSA were measured on Access2 or DxI800 analyzers (Beckman Coulter).

RESULTS

The percentage ratio of p2PSA to fPSA (%p2PSA) and Phi were significantly higher in all PCa subcohorts (positive initial or repeat biopsy result or negative digital rectal examination) (P < 0.0001) compared with patients without PCa. Phi had the largest area under the ROC curve (AUC) (AUC = 0.74) and provided significantly better clinical performance for predicting PCa compared with %p2PSA (AUC = 0.72, P = 0.018), p2PSA (AUC = 0.63, P < 0.0001), %fPSA (AUC = 0.61) or tPSA (AUC = 0.56). Significantly higher median values of Phi were observed for patients with a Gleason score ≥7 (Phi = 60) compared with a Gleason score <7 (Phi = 53; P = 0.0018). The proportion of aggressive PCa (Gleason score ≥7) increased with the Phi score.

CONCLUSIONS

The results of this multicenter study show that Phi, compared with tPSA or %fPSA, demonstrated superior clinical performance in detecting PCa at tPSA 1.6-8.0 μg/L (i.e., approximately 2-10 μg/L in traditional calibration) and is better able to detect aggressive PCa.

Immunoassay for the discrimination of free prostate-specific antigen (fPSA) forms with internal cleavages at Lys(₁₄₅) or Lys(₁₄₆) from fPSA without internal cleavages at Lys(₁₄₅) or Lys(₁₄₆)

Total levels of circulating prostate-specific antigen (tPSA) are strongly associated with prostate cancer (PCa) risk and outcome but benign prostate disease is the most frequent cause of a moderately elevated PSA level. Free PSA (fPSA) forms are independently associated with PCa risk and contribute modest diagnostic enhancements above and beyond tPSA alone. We developed an immunoassay for fPSA subfractions containing internal cleavages at Lys(145) or Lys(146) (fPSA-N). The assay was based on blocking intact single-chain fPSA (fPSA-I) with antibody 4D4 which does not detect PSA containing internal cleavages at Lys(145) or Lys(146). We also measured fPSA-N in blood from healthy volunteers and in anti-coagulated plasma from 76 men with or without evidence of PCa at biopsy. The analytical and functional detection limits of this assay were 0.016 ng/mL and 0.10 ng/mL, respectively. The median recovery of male fPSA-N from female plasma was 95.0%. All 12 female samples (average age 28 years) had fPSA-N concentrations at or below the analytical detection limit. The median fPSA-N concentration (0.050 ng/mL) in 9 healthy male volunteers (age<40 years) was below the functional detection limit, 0.420 ng/mL in 27 patients with benign prostate conditions and 0.239 ng/mL in 49 patients with PCa. Deming regression analysis of the patient samples showed that the measured fPSA-N concentrations were generally 23% lower than the previously calculated (fPSA minus fPSA-I) concentrations, likely due to differences in the antibody combinations used. In conclusion, we have developed a sensitive, specific and direct immunoassay for fPSA-N which can be used to study the clinical relevance of this PSA isoform.

Molecular biomarkers in prostate cancer

BACKGROUND

After more than two decades of clinical use, serum prostate-specific antigen (PSA) has increased the early diagnosis of prostate cancer, detecting the disease even when small volumes are present. Although stage migration of prostate cancer has occurred, PSA has well-known limitations, despite attempts at refinement and modification, such as the use of PSA velocity, which have been used to improve it. New biomarkers for prostate cancer have been discovered, with promising early results.

OBJECTIVE/METHODS

This article reviews the ubiquitous current literature on biomarkers in prostate cancer. A search using MEDLINE and EMBASE databases was performed and those articles reporting biomarkers in prostate cancer with clinically significant findings in terms of detection were analyzed. Immunohistochemical markers were not considered for this review.

RESULTS/CONCLUSION

Despite many markers being promising, no single marker has satisfied the criteria as a perfect candidate. Limited clinical use of IL-6, TGF-β1 and PCA3 has commenced, and further widespread availability of these tests is expected in the coming years. The future lies in artificial neural networks and panels of markers instead of individual assays. Although PSA has some well-known limitations, it is at present the best marker available for prostate cancer when used in conjunction with nomograms or risk calculators.

A panel of kallikrein markers can reduce unnecessary biopsy for prostate cancer: data from the European Randomized Study of Prostate Cancer Screening in Göteborg, Sweden

BACKGROUND

Prostate-specific antigen (PSA) is widely used to detect prostate cancer. The low positive predictive value of elevated PSA results in large numbers of unnecessary prostate biopsies. We set out to determine whether a multivariable model including four kallikrein forms (total, free, and intact PSA, and human kallikrein 2 (hK2)) could predict prostate biopsy outcome in previously unscreened men with elevated total PSA.

METHODS

The study cohort comprised 740 men in Göteborg, Sweden, undergoing biopsy during the first round of the European Randomized study of Screening for Prostate Cancer. We calculated the area-under-the-curve (AUC) for predicting prostate cancer at biopsy. AUCs for a model including age and PSA (the 'laboratory' model) and age, PSA and digital rectal exam (the 'clinical' model) were compared with those for models that also included additional kallikreins.

RESULTS

Addition of free and intact PSA and hK2 improved AUC from 0.68 to 0.83 and from 0.72 to 0.84, for the laboratory and clinical models respectively. Using a 20% risk of prostate cancer as the threshold for biopsy would have reduced the number of biopsies by 424 (57%) and missed only 31 out of 152 low-grade and 3 out of 40 high-grade cancers.

CONCLUSION

Multiple kallikrein forms measured in blood can predict the result of biopsy in previously unscreened men with elevated PSA. A multivariable model can determine which men should be advised to undergo biopsy and which might be advised to continue screening, but defer biopsy until there was stronger evidence of malignancy.

Why determine only the total prostate-specific antigen, if the free-to-total ratio contains the information?

Background

Total prostate-specific antigen (tPSA) is the best available test for the detection of prostate cancer but it lacks specificity. The free-to-total ratio (F/T ratio) is used to increase specificity in the range of tPSA of 4–10 µg/L.

Materials and methods

Four hundred and seven biopsy results and quantitative tPSA and F/T ratio data were combined. Using the histological determination, normal/hyperplasia versus malignant as a gold standard, receiver operating characteristic (ROC) curves as well as the areas under the curve (AUC) for tPSA and F/T ratio were determined. The differences between the two AUCs were considered for various tPSA ranges and specificities of F/T ratio and tPSA were calculated.

Results

In the total group, there was a gain of specificity of 11% (from 23% to 34%) when the sensitivity was 92% (using a cut-off >0.28 for the F/T ratio and a cut-off >4 µg/L for tPSA). When considering the group of patients for which the F/T ratio is currently used (4–10 µg/L), the gain of specificity was 27% (from 2% to 29%). This implicates that the number of unnecessary biopsies taken will be reduced by 27%. Moreover, the AUC of the F/T ratio was significantly higher at an even broader range of tPSA, i.e. up to 40 µg/L.

Conclusions

This study demonstrates that the F/T ratio has better diagnostic performance than tPSA, not only in the grey zone of tPSA, but also outside the grey zone, i.e. up to 40 µg/L.

PSA and other tissue kallikreins for prostate cancer detection

Prostate cancer is the most common neoplasia of middle-aged men. Prostate specific antigen (PSA) is the first FDA-approved tumour marker for early detection of cancer and it is now in widespread clinical use. The discovery of different PSA molecular forms in serum (free PSA, PSA complexed with various protease inhibitors) in the early 1990s renewed clinical research to enhance the specificity of PSA. Also, the use of a homologous prostate-localised antigen, human glandular kallikrein 2 (KLK2) may further reduce the number of unnecessary prostate biopsies. More recently, promising data is emerging regarding molecular forms of free PSA (proPSA, BPSA, 'intact' PSA) and other members of the expanded human kallikrein family. These new findings may add substantial clinical information for early detection of prostate cancer.

Circulating biomarkers for prostate cancer

Due to its significant applicability for early detection, risk prediction and follow-up evaluation, prostate specific antigen (PSA) has revolutionized our ability to treat prostate cancer patients. With the prevalent use of PSA for early detection during the last two decades, disease characteristics have been altered towards early detected, localized tumors with a high chance of cure following local therapy. This advantage faces the risk of overdetection and overtreatment. In addition, PSA lacks both, sensitivity and specificity to accurately detect patients at risk of prostate cancer. Therefore, novel biomarkers are urgently needed to improve identification of men at risk of having the disease and to predict the natural behaviour of the tumor. Recent advances in the evaluation of high-throughput technologies have led to the discovery of novel candidate markers for prostate cancer. This article will briefly discuss current PSA-based strategies and review several novel biomarkers for prostate cancer, detectable in blood.

Intact free prostate-specific antigen and free and total human glandular kallikrein 2. Elimination of assay interference by enzymatic digestion of antibodies to F(ab')2 fragments

Various blood constituents can interfere with immunoassays, usually by binding the Fc portion of antibodies. Our previously developed assays for intact free prostate-specific antigen (PSA), free human kallikrein 2 (hK2), and total hK2 frequently yielded falsely high results despite including an excess of scavenger antibodies. We investigated whether this interference could be eliminated by replacing monoclonal capture or tracer antibodies with F(ab')2 or recombinant Fab fragments. Female heparin plasma samples (n = 1092), which should have negligible PSA and hK2, and male samples (n = 957) were analyzed to identify samples manifesting interference, which then were used to optimize protocols for the immunoassays. We compared original assays (monoclonal antibodies) versus optimized assays (F(ab')2 fragments: denatured mouse IgG added as scavenger) using another set of EDTA plasma (n = 113), heparin plasma (n = 160), and serum samples (n = 171). With the original assays, the frequency of falsely elevated hK2 and intact free PSA was 15 and 13%, respectively. The optimized assays eliminated 70-85% of these falsely elevated results and importantly reduced the magnitude in the remainder. F(ab')2 fragmentation was the most important factor in reducing interference. The optimized intact free PSA, free hK2, and total hK2 assays manifested high accuracy close to the lower limit of detection.

Marqueurs biologiques du cancer de la prostate

Screening for prostate cancer is currently based on the assessment of blood prostate specific antigen (PSA). Although PSA was shown to be an adequate tool in prostate cancer screening, beginning from 4.0 ng/mL, its specificity is less significant. In men with a PSA between 4.0 and 10 ng/mL its predictive value is low. Therefore, there is a need for new instruments likely to improve the specificity of blood PSA levels between 4.0 and 10 ng/mL and the screening for prostate cancer in subjects with low PSA. Recent data are reviewed.

Innovations in serum and urine markers in prostate cancer current European research in the P-Mark project

An overview is given of serum and urine prostate cancer markers that are currently under investigation and subsequently the P-Mark project is introduced. There are many markers showing promise to overcome the limitations of prostate specific antigen (PSA). Eventually, these markers should be able to increase the specificity in diagnosis, differentiate between harmless and aggressive disease and identify progression towards androgen independence at an early stage. In the P-Mark project, several recently developed, promising markers will be evaluated using clinically well-defined biorepositories. Following successful evaluation, these markers will be validated on a sample set derived from two large, European, prostate cancer studies and used for the identification of special risk groups in the general population. In addition, novel markers will be identified in the same biorepositories by different mass spectrometry techniques.

Association of free-prostate specific antigen subfractions and human glandular kallikrein 2 with volume of benign and malignant prostatic tissue

BACKGROUND

We investigated the association of different subfractions of prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2), such as total PSA (tPSA), complexed PSA (cPSA), free PSA (fPSA), "single-chain Intact fPSA" (fPSA-I), "multi-chain nicked fPSA" (fPSA-N), and total hK2 with volumes of total prostate gland, transition zone (tz), and prostate cancer (PCa) tissue in patients with benign and malignant prostatic disease.

METHODS

Serum samples were collected from men with negative biopsy (n=164) and PCa (n=252). Total and fPSA were measured using a commercially immunoassay. We measured hK2 and fPSA-I by previously reported in-house research assays specific for hK2 and single-chain, non-cleaved fPSA, respectively. Levels of fPSA-N (=fPSA-fPSA-I) and cPSA (=tPSA-fPSA) were calculated. Total prostate and tz volume were measured using transrectal ultrasound (TRUS); PCa volume was calculated using a computer assisted volumetric program. Association with tz and cancer volumes (CaVols) was performed by linear regression analysis.

RESULTS

All PSA subfractions and hK2 were associated with tz volume in multivariable linear regression analysis. Only hK2, fPSA, and fPSA-N were significantly associated with CaVol in multivariable analysis, fPSA-I seemed to be cancer related.

CONCLUSIONS

The multi-chain fPSA-N subfractions of fPSA may be a valuable predictor of both benign prostate hyperplasia (BPH) and CaVol that is likely to be more useful in predicting tz volumes than CaVols. fPSA-I may provide information on cancer without being influenced by the presence of BPH.

Selective recognition of enzymatically active prostate-specific antigen (PSA) by anti-PSA monoclonal antibodies

Prostate-specific antigen (PSA) is widely used as a serum marker for the diagnosis of prostate cancer. To evaluate two anti-free PSA monoclonal antibodies (mAbs) as potential tools in new generations of more relevant PSA assays, we report here their properties towards the recognition of specific forms of free PSA in seminal fluids, LNCaP supernatants, 'non-binding' PSA and sera from cancer patients. PSA from these different origins was immunopurified by the two anti-free PSA mAbs (5D3D11 and 6C8D8) as well as by an anti-total PSA mAb. The composition of the different immunopurified PSA fractions was analysed and their respective enzymatic activities were determined. In seminal fluid, enzymatically active PSA was equally purified with the three mAbs. In LNCaP supernatants and human sera, 5D3D11 immunopurified active PSA mainly, whereas 6C8D8 immunopurified PSA with residual activity. In sera of prostate cancer patients, we identified the presence of a mature inactive PSA form which can be activated into active PSA by use of high saline concentration or capture by an anti-total PSA mAb capable of enhancing PSA activity. According to PSA models built by comparative modelling with the crystal structure of horse prostate kallikrein described previously, we assume that active and activable PSA could correspond to mature intact PSA with open and closed conformations of the kallikrein loop. The specificity of 5D3D11 was restricted to both active and activable PSA, whereas 6C8D8 recognized all free PSA including intact PSA, proforms and internally cleaved PSA.

Characterization of prostate-specific antigen binding peptides selected by phage display technology

Prostate-specific antigen (PSA) is an important marker for the diagnosis and management of prostate cancer. Free PSA has been shown to be more extensively cleaved in sera from benign prostatic hyperplasia patients than in sera from prostate cancer patients. Moreover, the presence of enzymatically activatable PSA was characterized previously in sera from patients with prostate cancer by the use of the specific anti-free PSA monoclonal antibody (mAb) 5D3D11. As an attempt to obtain ligands for the specific recognition of different PSA forms including active PSA, phage-displayed linear and cyclic peptide libraries were screened with PSA coated directly into microplate wells or presented by two different anti-total PSA mAbs. Four different phage clones were selected for their ability to recognize PSA and the inserted peptides were produced as synthetic peptides. These peptides were found to capture and to detect specifically free PSA, even in complex biological media such as sera or tumour cell culture supernatants. Alanine scanning of peptide sequences showed the involvement of aromatic and hydrophobic residues in the interaction of the peptides with PSA whereas Spotscan analysis of overlapping peptides covering the PSA sequence identified a peptide binding to the kallikrein loop at residues 82-87, suggesting that the peptides could recognize a non-clipped form of PSA. Moreover, the PSA-specific peptides enhance the enzymatic activity of PSA immobilized into microplate wells whereas the capture of PSA by the peptides inhibited totally its enzymatic activity while the peptide binding to PSA had no effect in solution. These PSA-specific peptides could be potential tools for the recognition of PSA forms more specifically associated to prostate cancer.

[PSA and benign prostatic hyperplasia]

In the opinion of many urologists, prostate-specific antigen (PSA), which is not specific of any disease, is not considered in the diagnosis and follow-up of benign prostatic hyperplasia (BPH). Nonetheless, prostate cancer diagnosis is based on PSA screening. PSA value is thus available for a majority of men above 50. Recent data suggest that there is a link between PSA value and BPH natural history, turning PSA into a tool for BPH management and prevention of complications such as retention. It hasn't got into practice so far, as recommended criteria for PSA screening in BPH have not been issued. The debate over this topic is only at its beginning.

Prostate-specific antigen and related isoforms in the diagnosis and management of prostate cancer

Despite its unparalleled merits for prostate cancer detection and staging, prostate-specific antigen (PSA) is not a marker for prostate cancer only, but also is expressed in benign conditions. For early detection, limitations of PSA are obvious. Its widespread use has led to an extensive amount of expensive and often unnecessary diagnostic procedures associated with significant morbidity. Total PSA derivatives may enhance the accuracy of prostate cancer diagnosis. The ratio of free-to-total PSA improves specificity while maintaining a high sensitivity for prostate cancer detection for men with a total PSA of 2.5 to 10 ng/mL. Human glandular kallikrein also has the potential to be a valuable tool in combination with total and free PSA for early diagnosis of prostate cancer. Complex PSA seems to be a reliable tool to improve specificity at high sensitivity levels in men with suspected prostate cancer (mainly in PSA levels below 4 ng/mL). Newly discovered isoforms of free PSA also may impact early detection of prostate cancer with encouraging preliminary results that warrant further clinical investigation.

Molecular diagnosis of prostate cancer

The diagnosis, staging, and management of prostate cancer as we know it today is greatly dependent on our ability to measure serum prostate-specific antigen (PSA) concentration. Nevertheless, because serum PSA concentration, particularly when less than 10 ng/mL, reflects the presence of benign prostatic hyperplasia more often than cancer, there is a clear need for more specific prostate cancer markers. The most promising new markers for prostate cancer are the various molecular forms of free PSA. Mass spectrometry also is emerging as a potential tool in prostate cancer screening. Because it is unlikely that any one marker will have 100% sensitivity and specificity, as new serum markers are tested, nomograms that incorporate multiple independently predictive parameters for the detection of prostate cancer will become indispensable in our efforts to improve prostate cancer screening.

A rational approach to benign prostatic hyperplasia evaluation: recent advances

PURPOSE OF REVIEW

In this article we aim to outline the recent advances in the evaluation of a patient with symptoms suggestive of benign prostatic hyperplasia. We define the role of the clinical evaluation and techniques that are evolving for the appropriate management of a patient with benign prostatic hyperplasia. Both non-invasive and invasive investigation techniques are reviewed.

RECENT FINDINGS

Initiating early and appropriate treatment is the primary aim of investigation for a patient with lower urinary tract symptoms. Both clinical history and examination and appropriate investigations are vital to establishing a diagnosis. Symptom scores, prostate specific antigen and prostate volume were found to closely relate in predicting the progression of benign prostatic hyperplasia and in recent years increased interest has centred on the progression of this disease principally related to the development of new pharmacotherapy. Despite these positive findings further research is needed to develop reliable tools to predict progression. Newer ultrasound techniques hold promise for the future. Conventional pressure flow studies have a defined role in excluding patients who are less likely to benefit from prostatic surgery by providing information on detrusor function; and non-invasive urodynamic techniques need further evaluation but appear to be promising.

SUMMARY

The minimal initial evaluation of a patient with benign prostatic hyperplasia should include a thorough history, digital rectal and neurological examinations, symptom scoring (including quality of life and sexual score) and measurement of serum prostate specific antigen. Other methods should be reserved for more complex situations. Attempts should be made at identifying those patients in whom the disease process is likely to progress.

Biology of prostate-specific antigen

The human kallikrein (hk) family, located on chromosome 19, encodes prostate-specific antigen (PSA [or hK3]), hK2, hK4, and hK15 (prostin), as well as other serine proteases. Although PSA has been used in the detection of prostate cancer for several years, much remains unknown about its function and forms. The regulatory mechanisms of PSA are vital to its understanding. A particular mechanism by which PSA forms complexes with either alpha1-antichymotrypsin or alpha2-macroglobulin may provide important information for disease detection and progression. Data are emerging that show that active hK2, hK4, and hK15 may be important to convert pro-PSA to the active PSA enzyme. This information, along with insights into the precise mechanisms of PSA expression, may be used to suggest that PSA and, perhaps, other members of the hK family contribute critical control mechanisms to tumor invasion or progression. Although much remains to be revealed on the role of these gene products in the detection and progression of prostate cancer, findings from studies that show sensitive signaling of the disease > or =20 years before the diagnosis of clinically significant prostate cancer may alter screening procedures and improve treatment options.

PSA markers in prostate cancer detection

The PSA revolution that has occurred over the previous 2 decades has positively impacted the detection and treatment of men with prostate cancer. Although methods to improve specificity have shown promise (eg, PSAD, age-specific PSA, and PSA velocity), meaningful interpretation has yet to be uniformly accepted within clinical practice. The identification of other molecular forms of PSA within serum has led to a new era in PSA markers. Initial application employing %fPSA has provided improved discrimination between benign and malignant prostatic disease; however, questions remain regarding the ultimate threshold value. The discovery of various free forms of PSA--such as proPSA, BPSA, and iPSA--also have introduced the potential for improved specificity in detection. Although early results are encouraging, further evaluation is anticipated. The development of improved methods to detect and measure cPSA has demonstrated provocative results, and exhibits the potential to replace PSA as a standard diagnostic test in cancer screening.