Measurement of the proportion of free to total prostate-specific antigen improves diagnostic performance of prostate-specific antigen in the diagnostic gray zone of total prostate-specific antigen

Three immunoassays based on monoclonal antibodies specific for prostate specific antigen (PSA), alpha-1-antichymotrypsin (ACT), and the PSA-ACT complex

BACKGROUND

Prostate specific antigen (PSA) has been widely used as a biomarker for the screening and diagnosis of prostate cancer. PSA in serum predominantly exists as a complex with alpha-1-antichymotrypsin (ACT), and measurement of free PSA and the PSA-ACT complex may improve the utility of the serum PSA assay for differential diagnosis of prostate cancer and non-malignant prostate diseases, such as benign prostatic hyperplasia (BPH).

METHODS

Monoclonal antibodies (MAbs) against PSA, ACT, and the PSA-ACT complex were produced by immunizing mice with an incubated mixture of PSA and ACT, and characterized by Western blot analyses and several enzyme-linked immunosorbant assay (ELISA) methods.

RESULTS

The MAbs produced in this study are capable of distinguishing the PSA-ACT complex from free PSA and ACT. Four MAbs have been selected and utilized to construct three ELISA systems for the separate measurements of free PSA, the PSA-ACT complex, and total PSA.

CONCLUSIONS

The three PSA assay systems developed in this study can specifically measure free PSA, total PSA, and the PSA-ACT complex with equal molar sensitivity. It is expected that these PSA assay systems could be useful in the diagnosis of prostate cancer.

Distribution and secretory pathways of prostate specific antigen, alpha1-antichymotrypsin and prostate secretory granules in prostate cancers

Using 19 radical prostatectomy specimens, we studied the histological distribution of free prostate specific antigen (PSA), total PSA, alpha1-antichymotrypsin (ACT) and prostate secretory granules (PSG) in both normal and cancerous cells of the prostate. After glutaraldehyde fixation, numerous fine eosinophilic droplets of PSG could be found mainly in the apical portions of normal acinous epithelial cells, but was markedly decreased in cancer cells. With antibodies against free PSA, normal acinous cells were granularly positive in the apical portion of the epithelium, which corresponded to the PSG, whereas cancer cells were diffusely positive. With antibodies against ACT, normal duct cells and cancer cells were often positive, but few normal acinous cells were positive. Presumably, these findings indicate that free PSA is secreted into the lumen as PSG in normal glands, but not by the same pathway in cancers where free PSA appears to accumulate due to a decrease of PSG, then leak into the blood producing complexed PSA to some extent in the cytoplasm. One factor analysis of variance (ANOVA) on the correlation of tumor differentiation or Gleason score with serum values of total PSA, free PSA and a free/total PSA ratio demonstrated no significant links. Elucidation of secretory mechanisms should provide better comprehension of various PSA indices for prostate cancer screening.

Early diagnosis and surgical management of prostate cancer

Prostate cancer is a significant cause of morbidity and mortality in the United States and Europe. The natural ageing of the population as well as the continued and widespread use of diagnostic tests such as prostate specific antigen (PSA), has led to an increase in the numbers of men diagnosed with localised prostate cancer. Screening to identify organ-confined disease has provoked much public and scientific attention, but remains controversial. Radical prostatectomy is one of the most challenging urological procedures performed. Improvements in technique due to better understanding of pelvic anatomy have reduced complications, with acceptable standards and excellent results in high-volume institutions. Continual refinements in technique and the recent introduction of laparoscopic radical prostatectomy are likely to improve functional outcome further. However the effectiveness of surgery in improving survival and quality of life, in men with early prostate cancer remains to be determined. The results from large randomised controlled trials are eagerly awaited.

The role of the complexed-to-total prostate-specific antigen ratio in predicting the final pathological stage of clinically localized prostate cancer

OBJECTIVES

To examine the association between the complexed-to-total (C:T) prostate-specific antigen (PSA) ratio and prostate cancer pathological stage to assess whether the C:T PSA ratio may predict the final pathological stage in patients with clinically localized prostate cancer.

PATIENTS AND METHODS

In a prospective study, 101 men with clinically localized prostate cancer underwent a staging pelvic lymphadenectomy and radical prostatectomy. Total PSA (tPSA) and PSA complexed to alpha(1)-antichymotrypsin (cPSA) were measured from preoperative plasma and were correlated with the clinical and pathological stage, and with surgical margin status. The pathological stage was determined as organ-confined (n=59) and extracapsular extension (n=42).

RESULTS

The distributions of tPSA and cPSA were significantly different in men with locally confined and those with locally extended disease. This finding was not observed for the C:T PSA ratio. The area under the receiver operating characteristic (ROC) curve to predict the final pathological stage was significantly greater for tPSA (0.684) and cPSA (0.677) than for the C:T PSA ratio (p<0.032). TPSA (0.685) and cPSA (0.670) also showed areas under the ROC curve greater than that of the C:T PSA ratio (0.542) (p<0.05) for prediction of positive surgical margins.

CONCLUSIONS

Our results show that the C:T PSA ratio does not improve the performance of total PSA for predicting the final pathological stage in patients with clinically localized prostate cancer.

Free prostate-specific antigen improves prostate cancer detection in a high-risk population of men with a normal total PSA and digitalrectal examination

OBJECTIVES

Uncertainty exists regarding optimal prostate cancer screening parameters for high-risk populations. The purpose of this study is to report the use of percent free prostate-specific antigen (PSA) as an indication for biopsy in men at increased risk for developing prostate cancer who have a normal digital rectal examination (DRE) and total PSA level between 2 and 4 ng/mL.

METHODS

African-American men and men with at least one first-degree relative with prostate cancer are eligible for enrollment into the Prostate Cancer Risk Assessment Program (PRAP) at our institution. Between October 1996 and April 2002, 310 asymptomatic high-risk men with no history of prostate cancer, benign prostatic hyperplasia (BPH), or prostatic intraepithelial neoplasia (PIN) were screened in the PRAP with DRE and total PSA. Percent free PSA was obtained in men with a total PSA between 2 and 10 ng/mL. Men with a normal DRE and total PSA between 2 and 4 ng/mL were advised to undergo transrectal ultrasound-guided (TRUS) biopsies of the prostate if the percent free PSA was less than 27%. Other indications for biopsy included an abnormal DRE or a total PSA greater than 4 ng/mL. The primary endpoint evaluated was prostate cancer detection in high-risk men with a benign prostate examination, a normal total PSA between 2 and 4 ng/mL, and percent free PSA less than 27%.

RESULTS

Of the 310 men, 174 (56%) were African American and 202 (65%) had at least one first-degree relative with prostate cancer. Sixty-two of the 310 men were referred for prostate biopsy, and 40 of 62 had biopsy performed. Twenty-one of 40 men were diagnosed with prostate cancer for a cancer detection rate of 53% in all men undergoing biopsy and an overall cancer detection rate of 6.8% in this high-risk population. Thirty-seven high-risk men (median age 54 years) with a total PSA level between 2 and 4 ng/mL (median 2.7 ng/mL) and a normal DRE were found to have a percent free PSA level of less than 27% (median 16%, range 8% to 25%). Twenty-three of these 37 men (62%) proceeded with the recommended prostate biopsy. Prostatic adenocarcinoma was diagnosed in 12 of 23 men for a cancer detection rate of 52% in men undergoing biopsy and 32% in all men with a normal DRE, a total PSA between 2 and 4 ng/mL, and a percent free PSA less than 27%. All positive biopsies demonstrated clinically significant Gleason score 6 or 7 disease. In all men electing radical prostatectomy, bilateral organ-confined disease (pT2bN0M0) was confirmed.

CONCLUSIONS

In this unique population of men at high risk for prostate cancer, a percent free PSA of less than 27% was found to be useful for detecting early-stage but clinically significant cancers in men with a total PSA value between 2 and 4 ng/mL and normal DRE findings.

Serum human glandular kallikrein (hK2) and insulin-like growth factor 1 (IGF-1) improve the discrimination between prostate cancer and benign prostatic hyperplasia in combination with total and %free PSA

BACKGROUND

There is growing evidence describing an association of hK2 and IGFs with cancer. The aim of this study is to investigate the differences in serum levels of hK2 and IGFs in a large group of patients with benign prostatic hyperplasia (BPH) or prostatic carcinoma (CaP) and to examine the value of these variables, as well as their various combinations with PSA, for discriminating between these two clinical entities.

METHODS

Human glandular kallikrein 2 (hK2), insulin-like growth factor-1 (IGF-1), free and total PSA concentrations were measured with non-competitive immunological procedures. Receiver operating characteristic (ROC) analysis as well as univariate and multivariate logistic regression analysis were performed to investigate the potential utility of the various markers and their combinations for discriminating between BPH and CaP.

RESULTS

hK2 and IGF-1 concentrations were increased in CaP patients, in comparison to BPH patients. hK2/free PSA and free/total PSA ratios (area under the curve, AUC = 0.70) were stronger predictors of prostate cancer than the IGF-1/total PSA ratio (AUC = 0.56) in the group of patients with total PSA <4 microg/L. The hK2/free PSA ratio (AUC = 0.74) was found to have significant discriminatory value in patients with total PSA within the "gray zone" (4-10 microg/L). Multivariate logistic regression models confirmed the observed relationships and identified IGF-1/free PSA and hK2/free PSA as independent predictors of CaP.

CONCLUSIONS

hK2/free PSA and IGF-1/free PSA ratios may be useful adjuncts in improving patient selection for prostate biopsy.

The relation of prostate biopsy results and ratio of free to total PSA in patients with a total PSA between 4-20 ng/mL

OBJECTIVE

In this study our aim was to investigate the efficacy of free to total PSA ratio in discrimination of benign prostate hyperplasia and prostate cancer.

MATERIALS AND METHODS

A total of 194 patients, 52 to 82 years old (mean 66.06 +/- 0.47 years) with PSA levels between 4 to 20 ng/mL were included into this study. Each patient underwent sextant prostate biopsy under transrectal ultrasound guidance. The patients were divided into two groups as PSA 4-10 and 10-20 ng/mL. Patients with benign and malign results were compared with respect to age, total PSA level, free PSA level and free/total (f/t) PSA ratio.

RESULTS

Biopsies revealed prostate cancer in 16 of 130 patients (12.3%) with serum PSA 4-10 ng/mL and in 10 of 64 patients (15.6%) with serum PSA 10-20 ng/ml. In both PSA groups free PSA and f/t PSA levels were statistically significant, where total PSA levels were not. In patients with 4-20 ng/mL total PSA levels and a cut off level of < 0.18 for f/t PSA, the sensitivity, specificity and positive predictive value for prostate cancer were 88.5%, 53.6% and 20.4% respectively.

CONCLUSION

Higher levels of PSA suggest prostate cancer, but still additional parameters are needed for patients with PSA 4-20 ng/mL, such as free PSA and f/t PSA. Although a cut off level of < 0.18 for f/t PSA seems to be the most accurate one to discriminate benign and malign diseases further studies on larger groups of patients are needed.

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

PURPOSE

Free prostate specific antigen (PSA) in serum consists of heterogeneous molecular subforms. Recently we developed an immunoassay for selective measurement of a subfraction of free PSA called intact PSA, which has been shown to be closely associated with prostate cancer. We assessed the ability of serum intact PSA to discriminate between benign and malignant prostatic disease.

MATERIALS AND METHODS

In serum of 178 men with benign disease and 255 men with prostate cancer we measured total PSA and free PSA using a commercially available immunoassay. Intact PSA levels were analyzed by a newly developed assay specific for noncleaved, that is single chain forms of free PSA. Internally cleaved "nicked" PSA was calculated by subtracting intact from free PSA. We also calculated ratios of intact PSA-to-free PSA (intact-to-free PSA) and nicked PSA-to-total PSA (nicked-to-total PSA). We compared means, medians and ranges of all analytes and ratios in patients with and without cancer for the entire total PSA range and in a subset with total PSA ranging from 2 to 10 ng./ml. Furthermore, various combinations of PSA forms were tested for their predictive ability. For statistical comparison we used the Mann-Whitney U test and ROC analysis.

RESULTS

The ratio intact-to-free PSA was significantly higher in cancer (median 48.5%) compared to noncancer cases (median 41.8%, p <0.0001). Conversely, the ratio nicked-to-total PSA was significantly higher in men without compared to those with prostate cancer (median 11.0% and 6.0%, respectively, p <0.0001). Highest discriminative ability was observed for a combination of intact, total and free PSA (log [intact, free, total], AUC = 0.773) followed by nicked-to-total PSA (AUC 0.755). In the subgroup of patients with total PSA levels from 2 to 10 ng./ml. only the AUC of log intact, free, total (AUC 0.706, p = 0.0017) and nicked-to-total PSA (AUC 0.704,p = 0.0019) were significantly larger compared to the AUC of total PSA (AUC 0.602).

CONCLUSIONS

By contrast to measuring crude free PSA concentration, selective determination of specific free PSA subforms, intact PSA and nicked PSA proved to be useful to discriminate men with benign from malignant prostatic disease. These markers may serve to generate specific serum profiles of PSA for improved specificity and early detection of prostate cancer. To translate the encouraging statistical advantage shown in this study into a clinically applicable tool warrants further investigation.

The free/total prostate-specific antigen ratio (%fPSA) is the best predictor of tumor involvement in the radical prostatectomy specimen among men with an elevated PSA

BACKGROUND

The relationship between the free-to-total prostate-specific antigen ratio (%fPSA) and prostate cancer (CaP) pathology remains controversial. Previous reports have shown a direct correlation between %fPSA and prostate volume as well as an indirect correlation between %fPSA and unfavorable CaP pathology, particularly among men with an elevated PSA. We evaluated the use of %fPSA to predict CaP pathology including percent of tumor involvement in the radical prostatectomy (RP) specimen.

METHODS

We prospectively analyzed 124 consecutive patients with CaP who underwent RP. In all patients, preoperative frozen serum was analyzed for assessment of %fPSA (Abbott Axsym). Pathologic review was performed using whole mount sections and total tumor volume was determined by planimetry. Statistical comparison between %fPSA and pathology was performed using log transformation.

RESULTS

Percent fPSA was indirectly correlated with prostate volume in both the entire group (N=124) and among those patients (N=87) with a total PSA >4 ng/mL (P<0.001). Overall, both %fPSA and total PSA also correlated with total tumor volume (P=0.03 and P=0.01, respectively) and Gleason sum (P<0.001 and P<0.01). When we evaluated the percent of tumor involvement (tumor density) defined as the volume of tumor per gland divided by total gland volume, for the entire population, both total PSA and %fPSA were predictive with equal significance (P<0.001). However, among the subset of patients with a PSA>4.0 ng/mL, there was only a significant correlation between tumor density and %fPSA as compared to total PSA (P<0.001 vs. P=0.06, respectively).

CONCLUSIONS

Independent of prostate volume, %fPSA is reflective of CaP pathology. Specifically, %fPSA was inversely correlated with tumor volume, Gleason sum and ECE. Among patients with modest PSA elevations, %fPSA was better than PSA in predicting percent of tumor involvement (tumor density) in the RP specimen.

The Proportion of Prostate-specific Antigen (PSA) Complexed to α1-Antichymotrypsin Improves the Discrimination between Prostate Cancer and Benign Prostatic Hyperplasia in Men with a Total PSA of 10 to 30 μg/L

Background: The aim of this study was to assess the diagnostic accuracy of the proportion of prostate-specific antigen (PSA) complexed to α1-antichymotrypsin (PSA-α1ACT:PSA ratio) in the differential diagnosis of prostate cancer (CaP) and benign prostatic hyperplasia (BPH) in men with total PSA of 10–30 μg/L.

Methods: We used our immunoassays (ELISAs) for total PSA and PSA-α1ACT complex to study 146 men. In 123, total PSA was between 10 and 20 μg/L; 66 of these had CaP and 57 BPH. In 23 men, total PSA was between 20 and 30 μg/L; 14 of these had CaP and 9 BPH. We calculated the area under the ROC curves (AUC) for total PSA, PSA-α1ACT complex, and PSA-α1ACT:PSA ratio, and determined the cutoff points that gave sensitivities approaching 100%.

Results: In the total PSA range between 10 and 20 μg/L, the AUC was significantly higher for the PSA-α1ACT:PSA ratio (0.850) than for total PSA (0.507) and PSA-α1ACT complex (0.710; P &lt;0.0001). A cutoff ratio of 0.62 would have permitted diagnosis of all 66 patients with CaP (100% sensitivity) and avoided 19% of unnecessary biopsies (11 of 57 patients). In the total PSA range between 20 and 30 μg/L, the AUC for the PSA-α1ACT:PSA ratio (0.980; 95% confidence interval, 0.82–0.99) was greater than the AUC for total PSA (0.750; 95% confidence interval, 0.51–0.89; P = 0.042). In this range, a cutoff point of 0.64 would have permitted the correct diagnosis of all 14 patients with CaP and 6 of the 9 with BPH.

Conclusions: The diagnostic accuracy of the PSA-α1ACT:PSA ratio persists at high total PSA concentrations, increasing the specificity of total PSA. Prospective studies with large numbers of patients are needed to assess whether the ratio of PSA-α1ACT to total PSA is a useful tool to avoid unnecessary prostatic biopsy in patients with a total PSA &gt;10 μg/L.

Using multiple cutpoints for the free-to-total prostate specific antigen ratio improves the accuracy of prostate cancer detection

BACKGROUND

Using a single cutpoint for the free-to-total (F/T) prostate specific antigen (PSA) ratio loses important diagnostic information. We evaluated the performance of multiple F/T PSA cutpoints in detecting prostate cancer in men with nonspecific PSA values.

METHODS

We extracted sensitivity and specificity data from 12 studies reporting on >or=30 cancer patients with PSA values between 2.0 and 10.0 ng/mL. We calculated stratum-specific likelihood ratios (LR) and areas under the receiver operating characteristic (ROC) curves.

RESULTS

Multiple cutpoints for the F/T PSA ratio significantly increased the area under the ROC (0.70) compared with the single investigator-selected cutpoint (0.62), P < 0.004. The LR for the most positive cutpoint stratum (2.62) was significantly higher than the LR for a positive test from the single cutpoint (1.36), P < 0.004.

CONCLUSIONS

Using multiple cutpoints increased the discriminating power of the F/T PSA ratio and led to greater probability revisions in the most positive test-result strata.

Prostate-specific antigen in prostate cancer: a case study in the development of a tumor marker to monitor recurrence and assess response

The serum marker known as prostate-specific antigen (PSA) has established itself as the most important tool for the early detection of prostate cancer. However, more recent data indicate that (post-treatment) PSA and PSA kinetics can be used to predict the outcome of a variety of therapeutic interventions including radical prostatectomy, radiation therapy, androgen deprivation, and treatment of hormone-refractory prostate cancer. PSA recurrence after radiation therapy is now accepted as a harbinger of developing metastatic disease. The American Society for Therapeutic Radiation Oncology (ASTRO) consensus definition is the most widely accepted definition of failure after radiation therapy. Rather than using a specific PSA cutoff, three consecutive PSA rises was felt to be a more reliable indicator of biochemical failure. The PSA nadir (the lowest PSA level achieved after therapeutic intervention) also appears to correlate with the likelihood of remaining disease-free. Similarly, a rapid doubling time is a significant predictor of developing distant metastases. The most appropriate definition for biochemical (PSA) failure following radical prostatectomy is usually considered to be a non-zero value. As is the case after radiotherapy, there appears to be a relationship between the rate of rise of the PSA and the risk of distant failure following radical prostatectomy. In patients with metastatic disease, multiple studies appear to indicate that a fall in PSA, however measured, appears to be predictive of improved outcome in prostate cancer patients treated with androgen deprivation. Multiple reports of trials in the treatment of hormone-refractory prostate cancer (HRPC) appear to substantiate the observation that patients who have a greater than 50% decline in PSA have an improved survival. Correlation of PSA declines with other markers of clinical benefit, including clinically significant "subjective" end points such as pain control, have strengthened the argument that a PSA decline can serve as an intermediate endpoint in clinical trials involving HRPC patients.

Early management of prostate cancer: how to respond to an elevated PSA?

Support for prostate cancer screening efforts is provided by observational studies reporting decreases in prostate cancer-specific mortality in areas where screening is performed with digital rectal exam (DRE) and measurement of serum prostate-specific antigen (PSA) levels. The combination of PSA and DRE is an excellent cancer-screening tool with sensitivity and positive predictive value superior to that of mammography and breast exam. Use of percent free PSA further improves the specificity of PSA testing, particularly in the range of 4-10 ng/ml, at which most false positive PSA tests occur. Men older than 50 with a >10-year life expectancy should be considered for prostate cancer screening. Those with an abnormal DRE or a PSA above 4 ng/ml should be referred to a urologist for further discussion of the risks and benefits of a prostate biopsy. Furthermore, those with a significant change in either DRE or PSA results, or those at higher risk for prostate cancer with a PSA level above 2.5 ng/ml, should also be referred for evaluation.

Thiophilic interaction chromatography facilitates detection of various molecular complexes of prostate-specific antigen in biological fluids

BACKGROUND

It is known that total PSA values are often greater than the sum total of free-PSA (f-PSA) and PSA-ACT complex. It is primarily because other PSA complexes are present in the patient serum and currently cannot be quantified. Our studies were aimed in developing methodology that will permit recovery of all molecular forms of PSA from various biological fluids.

METHODS

Thiophilic interaction (3S,T-gel) chromatography procedure was used to isolate various PSA molecular forms present in biological fluids. f-PSA and PSA complexes were shown to have strong affinity for T-gel. PSA forms eluted from the column were analyzed by SDS-PAGE/Western blot and were identified by immunostaining with antibody-specific to PSA and to various protease inhibitors. The identity of PSA complexes was also confirmed by Enzyme-linked Immunosorbent-assay (ELISA).

RESULTS

One step affinity chromatography procedure (3S,T-gel) was used to isolate different molecular forms of PSA in seminal plasma, patient sera, and in prostate cancer cell culture medium. Seminal plasma was shown to contain f-PSA, PSA-ACT, PSA-A2M, and PSA-PCI. Sera from prostate cancer patients at different stages of the disease contained f-PSA, PSA-ACT, and PSA-A2M. Besides these PSA forms, some patients at late stage of the disease (T3 and T4) also contained two additional PSA-complexes that have not been identified as of yet. Conditioned medium from LNCaP cells was shown to contain f-PSA, PSA-ACT, and PSA-A2M complexes.

CONCLUSIONS

Thiophilic gel has strong affinity for all known molecular forms of PSA present in any biological material. Visualization of PSA molecular forms in Western-blot analysis was feasible only after patient serum was processed through T-gel. Our procedure can be used to screen hybridoma and antibodies specific to the individual PSA complex. The PSA molecular forms isolated from patient serum after T-gel procedure may provide useful internal calibrators, and thus may significantly enhance the reliability of PSA measurements.

Combined Use of Prostate-Specific Antigen Derivatives Decreases the Number of Unnecessary Biopsies to Detect Prostate Cancer

The authors evaluated the prostate cancer detection rate in Turkish patients with prostate-specific antigen (PSA) levels of 4 ng/ml to 10 ng/ml and who had normal digital rectal examination (DRE) findings. They also aimed to evaluate the value of PSA density and percent free PSA in minimizing unnecessary prostate biopsies for these PSA ranges. This prospective study included 134 consecutive men referred for early prostate cancer detection or lower urinary tract symptoms. All men underwent transrectal ultrasound with systematic sextant needle biopsies. The ability of PSA density and percent free PSA to improve the power of PSA in the detection of prostate cancer was evaluated with statistical analyses as well as receiver operating characteristics curves. Among the 134 men, 124 (92.5%) had a benign histology and 10 (7.5%) had cancer diagnosed on the initial biopsies. Despite the disappointing results in regard to the sensitivity and specificity of PSA derivatives alone, the combination of PSA density and percent free PSA significantly increased the area under the curve compared with the use of each test alone. To increase the specificity of PSA in this patient population, the authors recommend combining two PSA derivatives in deciding whether to perform a biopsy. In a PSA range of 4 ng/ml to 10 ng/ml and with normal DRE, a percent free PSA < 21% and a PSA density > 0.18 yields highest specificity with 90% sensitivity.

Production of an anti-prostate-specific antigen single-chain antibody fragment from Pichia pastoris

Prostate-specific antigen (PSA) is a widely used marker for screening and monitoring prostate cancer. Because PSA levels are normally quite low, an antibody-based assay must be used to detect PSA. However, not all PSA-specific antibodies bind equally well to PSA or to its different isoforms. Therefore, a better understanding of how PSA interacts with PSA-specific antibodies is of considerable clinical interest. B80.3 is a widely used murine monoclonal anti-PSA antibody (IgG), which has very high affinity for both free and alpha-anti-chymotrypsin complexed PSA. More importantly, its gene sequence is known-making it one of only two anti-PSA antibodies that has been fully cloned and sequenced. To better elucidate the interaction between PSA and B80.3, a single-chain antibody fragment, derived from the variable domain of B80.3 (scFvB80), was cloned into a pPIC9 vector and expressed in Pichia pastoris. The secreted protein was purified using a three-step protocol beginning with a 50% ammonium sulfate precipitation step, followed by a T-gel thio-affinity step and concluding with a simple anion-exchange (DE52) filtration step. NMR studies indicate the protein is correctly folded while competitive enzyme-linked immunosorbant assays show that the purified scFvB80 has approximately 20% of the activity of the full-length B80.3 antibody. The protocol described here provides a quick and convenient route to prepare large quantities of very pure anti-PSA antibody fragments (15-20 mg/L culture medium) for detailed structural and biophysical characterization.

Separation methods applicable to prostate cancer diagnosis and monitoring therapy

During the last decade, significant research has been conducted using prostate-specific antigen (PSA) in the basic and clinical sciences and many advances have occurred in the clinical use of PSA for detecting and monitoring prostate cancer (PCa). Separation methods including gel-permeation chromatography, isoelectric focusing, lectin-affinity chromatography, polyacrylamide gel electrophoresis and high-performance liquid chromatography have made significant contributions to the discovery and identification of different molecular forms of PSA. Furthermore, the measurement of free and total PSA has improved the ability of PSA to detect early PCa. However, unnecessary biopsies are still needed for men with slightly elevated PSA values. On the other hand, PSA is not adequate for staging newly diagnosed PCa and prognosticating the course in individual cases. The possible application of separation methods in the basic science of prostate cancer may be associated with identification of more cancer-specific forms of PSA and discoveries of other serum proteins useful not only for detecting, but also for staging and prognosticating PCa. Such novel markers might lead to a better understanding of PCa aggressiveness and to developments in the clinical field of treatment.

The role of molecular forms of prostate-specific antigen (PSA or hK3) and of human glandular kallikrein 2 (hK2) in the diagnosis and monitoring of prostate cancer and in extra-prostatic disease

Prostate-specific antigen (PSA or hK3) is a glandular kallikrein with abundant expression in the prostate that is widely used to detect and monitor prostate cancer (PCa), although the serum level is frequently elevated also in benign and inflammatory prostatic diseases. PSA testing is useful for early detection of localized PCa and for the detection of disease recurrence after treatment. However, PSA has failed to accurately estimate cancer volume and preoperative staging. There is no PSA level in serum that definitively distinguishes men with benign conditions from those with prostate cancer, although PCa is rare in men with PSA levels in serum < 2.0 ng/ml. This prompted searches for enhancing parameters to combine with PSA testing, such as PSA density, PSA velocity, and age-specific reference ranges. Due to the protease structure, PSA occurs in different molecular forms in serum and their concentrations vary according to the type of prostatic disease. Human glandular kallikrein 2 (hK2) is very similar to PSA, but expressed at higher levels in prostate adenocarcinoma than in normal prostate epithelium. Blood testing for hK2 combined with different PSA forms improves discrimination of men with benign prostatic disease from those with prostate cancer. Many data have also been reported on the extra-prostatic expression of both PSA and hK2, and it is now believed that they may both have functions in tissues outside the prostate.

Thiophilic interaction chromatography of prostate-specific antigen

Prostate-specific antigen (PSA) protein and complexes of PSA with alpha1-antichymotrypsin (PSA-ACT) or alpha2-macroglobulin (PSA-A2M) prepared in vitro, have strong affinity for different thiophilic gels (T-gel). Free PSA, and these PSA complexes can be isolated due to their affinity for T-gels. The average recovery of PSA from several of the T-gels, based upon ELISA measurements, was 84 to 94%. The data suggest that T-gel affinity can be explored for the purification of free and complexed PSA from various biologic fluids.

Measurement of Circulating Forms of Prostate-specific Antigen in Whole Blood Immediately after Venipuncture: Implications for Point-of-Care Testing

Background: The purpose of this study was to validate the use of whole-blood samples in the determination of circulating forms of prostate-specific antigen (PSA).

Methods: Blood samples of hospitalized prostate cancer and benign prostatic hyperplasia patients were collected and processed to generate whole-blood and serum samples. Three different rapid two-site immunoassays were developed to measure the concentrations of total PSA (PSA-T), free PSA (PSA-F), and PSA-α1-antichymotrypsin complex (PSA-ACT) to detect in vitro changes in whole-blood samples immediately after venipuncture. The possible influence of muscle movement on the release of PSA from prostate gland was studied in healthy men by measuring the rapid in vitro whole-blood kinetics of PSA forms before and after 15 min of physical exercise on a stationary bicycle.

Results: Rapid PSA-T, PSA-F, and PSA-ACT assays were designed using a 10-min sample incubation. No significant changes were detected in the concentrations of PSA-T, PSA-F, and PSA-ACT from the earliest time point of 12–16 min compared with measurements performed up to 4 h after venipuncture. Physical exercise did not influence the concentrations of the circulating forms of PSA. Hematocrit-corrected whole-blood values of PSA-T and PSA-F forms were comparable to the respective serum values. Calculation of the percentage of PSA-F (PSA F/T ratio × 100) was similar irrespective of the sample format used, i.e., whole blood or serum.

Conclusions: We found that immunodetectable PSA forms are likely at steady state immediately after venipuncture, thus enabling the use of anticoagulated whole-blood samples in near-patient settings for point-of-care testing, whereas determinations of PSA (e.g., PSA-T, PSA-F, or PSA-ACT) performed within the time frame of the office visit would provide results equivalent to conventional analyses performed in serum.

[PSA:alpha 1-antichymotrypsin ratio/total PSA in the diagnosis of prostatic cancer in the range of total PSA from 4 to 10 ng/ml]

OBJECTIVE

To evaluate the usefulness of the ratio PSA:alpha-1-antichymotrypsin/total PSA (C/T) in the diagnosis of prostate cancer in the range of total PSA between 4 and 10 ng/mL.

MATERIAL AND METHODS

By using home-made ELISAs we have determined plasmatic concentrations of total PSA and complex PSA:alpha-1-ACT in 300 patients with total PSA between 4-10 ng/mL. All samples were obtained before any manipulation that could interfere the PSA levels.

RESULTS

By prostatic biopsy 85 patients (28.3%) were diagnosed of prostate cancer (CaP) and 215 (71.6%) of benign prostatic hyperplasia (BPH). The mean values of the complex PSA:alpha-1-ACT (4.2 ng/mL in the BPH patients vs 5.0 ng/mL in the CaP patients) and of the C/T ratio (0.70 vs 0.82, respectively) showed significant differences between both groups (p = < 0.0001). The total PSA did not show differences (6.1 ng/mL vs 6.0 ng/mL; p = 0.79). From all three parameter evaluated, the ratio C/T had the biggest area under the ROC (0.884) and statistically significant differences in comparison with total PSA (0.490; p = < 0.001) and the complex PSA:alpha-1-ACT (0.696: p = < 0.001). Therefore, by using a ratio C/T > 0.62 to decide the performance of a biopsy, 27% of the patients with BPH could have avoided this procedure with a 100% sensitivity. Increasing the ratio to 0.68 the specificity is 47% and the sensitivity is 95.2%. Rectal examination did not have influence on the cut-off, sensitivity, specificity and area under the ROC of the ratio C/T.

CONCLUSIONS

Our results confirm that the ratio C/T improve the diagnostic capacity of the total PSA between 4-10 ng/ml. Moreover, the rectal examination does not influence the selection of ratio C/T cut-off suggestives of CaP neither the diagnostic efficacy.

[Determining factors in the presence of carcinoma in prostate biopsies]

PURPOSE

Prostate biopsy is the diagnostic method to detect prostate carcinoma. We try to identify the optimal PSA cut-off, biopsy indication and the clinico-pathological characteristics in order to differentiate those patients with negative biopsy in which we should repeat the proceeding.

METHOD

We study 344 biopsies in 292 patients for 16 months. An univariate and multivariate study to identify the influent factors in the existence of prostate cancer in the first biopsy and in the patients with a second one was taken place.

RESULTS

Patients in the first biopsy Univariate study: Out of these variables (PSA, PSA ratio, digital rectal examination and prostate volume) just the PSA has statistical significance. Multivariate study: Only the the PSA is an indepent influence factor. Receiving Operated Curve: The optimal cut-off is 10.5 ng/ml. Patients with a second biopsy Univariate study: None of the variables is related with the existence of prostate cancer. Groups comparison: A comparison between the patients in the first biopsy and the patients with a second biopsy is performance with no statistical differences in the variables already mentioned.

CONCLUSION

The patient with a PSA greater than 4 ng/ml should be perform a prostate biopsy, mostly if his PSA is over 10 ng/ml. In our experience we do not related the need of a second biopsy with any factor in particular, therefore in our opinion and because of the high rate of negative false, all of the patients should be controlled and undergo a second biopsy if any change in PSA or clinics modification takes place.

Using the free-to-total prostate-specific antigen ratio to detect prostate cancer in men with nonspecific elevations of prostate-specific antigen levels

BACKGROUND

Prostate-specific antigen (PSA) levels between 4.0 to 10.0 ng/ml have poor specificity in prostate cancer screening, leading to unnecessary biopsies.

OBJECTIVE

To determine whether the free-to-total PSA ratio (F/T PSA) improved the diagnostic accuracy of these nonspecific PSA levels.

MEASUREMENTS AND MAIN RESULTS

MEDLINE searchedwas from 1986 to 1997. Additional studies were identified from article bibliographies and by searching urology journals. Two investigators independently identified English-language studies providing F/T PSA ratio test-operating characteristics data on > or = 10 cancer patients with PSA values between 2.0 and 10.0 ng/ml. Twenty-one of 90 retrieved studies met selection criteria. Two investigators independently extracted data on methodology and diagnostic performance. Investigator-selected cut points for the optimal F/T PSA ratio had a median likelihood ratio of 1.76 (interquartile range, 1.40 to 2.11) for a positive test and 0.27 (0.20 to 0.40) for a negative test. Assuming a 25% pretest probability of cancer, the posttest probabilities were 37% following a positive test and 8% following a negative test. The summary receiver operating characteristic curve showed that maintaining test sensitivity above 90% was associated with false positive rates of 60% to 90%. Methodologic problems limited the validity and generalizability of the literature.

CONCLUSIONS

A negative test reduced the posttest probability of cancer to approximately 10%. However, patients may find that this probability is not low enough to avoid undergoing prostate biopsy. The optimal F/T PSA ratio cut point and precise estimates for test specificity still need to be determined.

The changing scenario in diagnosing prostate cancer

Fifty patients were evaluated for serum total PSA (Prostate Specific Antigen), free PSA (f-PSA), free/total PSA ratio (f/t PSA ratio) and TPS(TM) (Tissue Polypeptide Specific Antigen). Fifty patients were clinically evaluated and categorized into BPH (benign prostatic hypertrophy) and CaP (carcinoma prostate) with twenty-five in each category before the serological examination. Serum total PSA concentration is elevated in 80% of BPH cases while it was elevated in all cases of CaP. With total PSA>10ng/mL, f/t PSA ratio was not applicable. For TPS(TM), a cell proliferation marker these values were 32% and 92% respectively. The advanced cases of CaP were reflected by the pronounced elevations of PSA and TPS(tM) while f/t PSA ratio was much below the cut-off limit (cut-off limit=0.14). The data suggest that whentotal PSA concentration <10ng/mL, f/t PSA ratio plays a very important role in discriminating BPH and CaP. However, TPS(TM) can be used as a valuable adjunct in diagnosis and follow-up of prostate cancer patients, especially in differentiating benign from malignant cases.

Clinical implications of free-to-total immunoreactive prostate-specific antigen ratios

OBJECTIVE

A study was performed to evaluate the free-to-total prostate-specific antigen (PSA) ratio for discriminating benign prostatic hyperplasia (BPH) or prostate cancer in the intermediate PSA range (2.0-10.0 microg/l) in patients referred for prostate evaluation. In addition, the relationship of free-to-total PSA ratio and tumor grade in prostatic cancer cases, implying a higher concentration of complex PSA in poorly differentiated cancer, was assessed for its predictive value of tumor aggressiveness at the time of diagnosis.

PATIENTS AND METHODS

Seven hundred and sixteen patients referred to the out-patient clinics of two urological departments were included in this prospective study. Blood samples were taken for total immunoreactive and free PSA (IMMULITE) determinations prior to any manipulation. The patients were grouped according to their PSA levels: 2.0-4.0 microg/l, 4.0-10.0 microg/l, 10.0-20.0 microg/l and > or = 20.0 microg/l. All patients were categorized, after histological confirmation, as having BPH (n = 423) or prostate cancer (n = 293). In patients with cancer the tumor grade was also assessed.

RESULTS

In patients with serum immunoreactive PSA levels in the 2.0-4.0 microg/l range, a free-to-total PSA ratio lower than 22% predicted the presence of prostate cancer with a sensitivity of 67% and a specificity of 63%. The positive- and negative-predictive values were 29% and 90% respectively. Receiver-operating characteristic curve analysis indicated a free-to-total PSA ratio of 22% to be the optimum discriminatory level in this low PSA range. For patients with a serum PSA level between 4.0 and 10.0 microg/l, the threshold ratio of 18% gave a sensitivity of 70%, a specificity of 70%, a positive-predictive value of 46% and a negative-predictive value of 87%. Men with a well differentiated grade of prostate cancer had higher free-to-total PSA ratios than those with less differentiated tumors (p = 0.01).

CONCLUSIONS

Our data indicate that the free-to-total PSA ratio, in patients with prostatic disease and with PSA levels in the 2.0-10.0 microg/l range, gives a significant improvement in prediction of cancer over the total immunoreactive PSA value alone. Because of the correlation between a higher tumor grade and a lower free-to-total PSA ratio, this ratio may be helpful in assessing the risk of a poorly differentiated cancer.

The role of free prostate-specific antigen in prostate cancer detection

Prostate-specific antigen (PSA) is the most important serum tumor marker for prostate cancer detection. Free PSA is one of the many molecular forms of PSA that have been identified. Percent free PSA improves the specificity (elimination of unnecessary biopsies) for prostate cancer detection in men with nonsuspicious digital prostate examination and total serum PSA ranges between 4 and 10 ng/mL. Further study is necessary to determine the optimal clinical utility of percent free PSA in men with a total serum PSA level of less than 4 ng/mL. In addition, the level of free PSA may be affected by many factors, including age, prostate volume, prostate manipulation, sample handling, and type of assay used.

Comparison of the percent free prostate-specific antigen levels in the serum of healthy men and in men with recurrent prostate cancer after radical prostatectomy

The percentage of free PSA in serum is currently used to better discriminate between patients with prostate cancer and patients with benign prostatic hyperplasia, in prostate cancer screening programs. We measured using non-competitive immunological techniques, the total PSA and free PSA in post-surgical serum of prostate cancer patients who underwent radical prostatectomy and then relapsed. We compared these data with those of a group of 40 age-matched men with no evidence of prostatic disease. Although in general, patients with prostate cancer had lower percentage of free PSA in serum in comparison to the controls, a subset of these patients (approximately 20%) had percent free PSA significantly higher than the levels considered as exclusive of prostate cancer in screening programs. We also found that percent free PSA does not correlate significantly with most of the standard clinical or pathological indicators of prostate cancer aggressiveness. Only a weak negative association with Gleason Score was observed. The percent free PSA in serum of relapsing prostate cancer patients varies within a relatively wide range and does not correlate significantly with indicators of cancer aggressiveness. The use of percent free PSA for excluding prostate cancer in screening programs must be approached with caution until the mechanism of low percent free PSA in the majority but not all prostate cancer patients is elucidated.

Identification of a superimmunoglobulin gene family member overexpressed in benign prostatic hyperplasia

BACKGROUND

Benign prostate hyperplasia (BPH), a nonmalignant disease with an increasing rate of occurrence associated with advancing age, requires auxiliary markers to help identify its presence and distinguish its progression from prostate cancer.

METHODS

Hybridoma technology was used to generate an antibody against a BPH antigen, which was subsequently characterized by Western blot analysis, sequence homology, and RT-PCR.

RESULTS

A BPH-associated protein, designated P25/26, was identified that showed a strong sequence similarity with superimmunoglobulin family members, overexpressed in BPH, with lower expression observed in both normal and prostate cancer tissues.

CONCLUSIONS

Further studies appear warranted to assess the role that this and other superimmunoglobulin family members may have in the pathogenesis of BPH, and to determine if these glycoproteins have any clinical utility in the differential diagnosis or therapeutic monitoring of BPH.

Ratio of Free or Complexed Prostate-specific Antigen (PSA) to Total PSA: Which Ratio Improves Differentiation between Benign Prostatic Hyperplasia and Prostate Cancer?

Background: The aim of this study was to compare the diagnostic utility of a new assay that measures all forms of prostate-specific antigen complexed (cPSA) to serum proteins except α2-macroglobulin with the assay of free PSA (fPSA) and the corresponding ratios to total PSA (tPSA) to improve the differentiation between benign prostatic hyperplasia (BPH) and prostate cancer (PCa).

Methods: Serum samples were collected from 91 men without prostate disease and with normal digital rectal examination (controls), 144 untreated patients with PCa, and 89 patients with BPH. tPSA and cPSA were measured using the Bayer Immuno 1 system; fPSA and the additional tPSA were measured with the Roche Elecsys system.

Results: The median cPSA/tPSA, fPSA/tPSA, and fPSA/cPSA ratios were significantly different between patients with BPH and PCa (78.7% vs 90.7%, 25.5% vs 12.1%, and 36.8% vs 14.3%, respectively; P &lt;0.001). No correlations of cPSA and its ratios to tumor stage and grade were found. ROC analysis showed that cPSA was not different from tPSA (areas under the curve, 0.632 vs 0.568), whereas the cPSA/tPSA ratio was similar to the fPSA/tPSA ratio in increasing discrimination between BPH and PCa patients with tPSA concentrations in the tPSA gray zone between 2 and 10 μg/L (areas under the curve, 0.851 vs 0.838).

Conclusions: Compared with tPSA, the fPSA/tPSA and cPSA/tPSA ratios both improve the differentiation between BPH and PCa comparably and are similarly effective in reducing the rate of unnecessary biopsies, whereas cPSA alone does not have any effect.

Prostate-specific antigen

Prostate-specific antigen (PSA) has revolutionized the diagnosis and management of men with prostate cancer. Significant advances have been made since the early development of immunoassays. While PSA is useful for staging and monitoring of established disease, it has shown the greatest utility in the realm of early detection realm. PSA is the most important tumor marker; its importance in evaluating men for the possibility of prostate cancer is irrefutable. Enhancing specificity is a pressing need. In this regard, the recognition of the molecular forms of free PSA and complex PSA have shown the most promise and undoubtedly will result in fewer false-positive PSA test results. The salient literature is reviewed and commentary made on the current status of PSA with particular emphasis on methods to enhance its specificity in early detection and applications.

Prostate-specific antigen in acute hepatitis and hepatocellular carcinoma

BACKGROUND

Prostate-specific antigen (PSA) is the most important tumor marker in prostate cancer diagnosis and follow-up. Its catabolism by the liver has not influenced its use as a prostate marker until the recent report of a significant increase in a man and a woman with acute hepatitis. In addition, PSA was detected in liver tumor extracts, which warranted its evaluation in liver cytolysis and hepatocellular carcinoma. In this study, PSA was evaluated in a cohort of both sexes presenting either acute hepatitis or hepatocellular carcinoima.

METHODS

Forty-two patients with acute hepatitis (21 male patients, 21 female patients) and 54 patients with hepatocellular carcinoma (31 male patients, 23 female patients) were tested for PSA by equimolar immunoassay (Abbott AxSYM Total PSA, Abbott Diagnostics, Rungis, France) and for relevant liver biological parameters (alpha-fetoprotein, alanine aminotransferase, aspartate aminotransferase, total bilirubin, and prothrombin rate).

RESULTS

PSA was undetectable in all the female patients and was consistent with age in the males (PSA median and range in acute hepatitis, 0.36 microg/l (range, 0.05-1.3); in hepatocellular carcinoma, 0.36 microg/l (range, 0.02-3.9)). It did not correlate with alpha-fetoprotein and aminotransferases.

CONCLUSIONS

Our results confirm the well-established reliability of PSA, and show that PSA remains a valid prostate marker in patients with acute hepatitis and hepatocellular carcinoma.

Treatment with soybean-derived Bowman Birk inhibitor increases serum prostate-specific antigen concentration while suppressing growth of human prostate cancer xenografts in nude mice

BACKGROUND

Bowman Birk inhibitor (BBI) is an anticarcinogenic serine protease inhibitor that may inhibit the protease activity of prostate-specific antigen (PSA) and the growth of human prostate cancer xenografts in nude mice.

METHODS

Human prostate cancer xenografts were established by implanting LNCaP cells into the prostate glands of NCRNU-M athymic nude mice. The animals with established tumors were maintained on a control diet or diets supplemented with 1% BBI or 1%, 2%, or 3% BBI concentrate (BBIC) for 6 weeks. The serum PSA concentrations were determined before and after the BBI or BBIC treatment period. The final tumor loads were determined at autopsy.

RESULTS

Treatment with BBI or BBIC decreased the final tumor load and increased the tumor doubling time and PSA density in the nude mice bearing human prostate cancer xenografts.

CONCLUSIONS

BBI and/or BBIC could be useful for prostate cancer treatment.

The prognostic value of different forms of prostate specific antigen and their ratios in patients with prostate cancer

OBJECTIVE

To assess the prognostic value for patient survival of different forms of PSA and ratios thereof, before treatment for prostate cancer, by considering the forms and ratios both as independent markers and by comparing them with other commonly used prognostic markers, e.g. tumour grade, local stage (T-stage) and absence or presence of skeletal metastases (M-stage).

PATIENTS AND METHODS

Blood samples were collected consecutively from men diagnosed with prostate cancer at our department in 1988. From this group, 66 men were followed until death, or for >/=9 years. Twenty-five patients died from their prostate cancer and 21 from other causes during the follow-up period. Forty-eight patients received hormonal treatment, whereas 18 remained untreated or received no treatment for their cancer before they died from other causes. Assays measuring the serum levels of free prostate specific antigen (fPSA), PSA complexed to alpha1-antichymotrypsin (PSA-ACT), and total PSA (tPSA) were used to calculate the percentage of free to total PSA (f/tPSA) fPSA/ACT and ACT/tPSA at diagnosis. Based on the initial levels or ratios of the PSA forms, the patients were divided into three numerically comparable groups (tertiles) for survival analysis. Prognostic factors predicting patient survival were evaluated using univariate (Kaplan-Meier life-tables with the log-rank test) and multivariate techniques (Cox proportional hazards regression model).

RESULTS

Univariate analysis using the log-rank test showed that the serum level of each molecular form of PSA, i.e. tPSA (P=0.001), PSA-ACT (P<0.001) and fPSA (P<0.001), as well as grade (P<0.001), T-stage (P=0.00355) and M-stage (P<0.001), provided statistically significant prognostic information. Log-rank tests showed that none of the ratios, i.e. f/tPSA, fPSA/ACT and ACT/tPSA, were informative of prognosis (P>0.05). However, in a multivariate analysis regression model, not only M-stage (risk ratio 4.2; P=0. 026) and grade (risk ratio 2.6; P=0.022), but also f/tPSA (risk ratio 1.8; P=0.037), provided significant prognostic information.

CONCLUSION

The values of tPSA, fPSA and PSA-ACT, as well as grade and T- and M-stage, are all independent prognostic factors of prostate cancer survival. In a multivariate analysis, not only M-stage and grade but also f/tPSA provided significant prognostic information.

The stability of free and bound prostate-specific antigen

OBJECTIVE

To determine if the assay for free prostate specific antigen (fPSA) and the calculated ratio of fPSA to total PSA (f/tPSA) is stable in conditions likely to be met in routine clinical practice.

MATERIALS AND METHODS

Two blood samples were obtained from 27 patients attending a routine urology clinic. Sample 1 was centrifuged immediately, assayed for fPSA and tPSA, and the f/tPSA calculated. This sample was then stored at 4 degrees C for 24 h, 48 h and 1 week, or at -20 degrees C for 24 h, 1 week and 1 month before the assays for fPSA and tPSA were repeated. The second sample was left at room temperature for 24 h before assay and processing, as for sample 1.

RESULTS

tPSA is a highly stable analyte; if whole blood samples are processed immediately, fPSA is stable for 24 h at 4 degrees C and 1 month at -20 degrees C. There was a significant reduction in the calculated f/tPSA in samples stored for >/=24 h at 4 degrees C (P<0.01); if the sample was stored at -20 degrees C the calculated f/tPSA was stable. After 24 h storage at room temperature, fPSA decreased by 6.3% and f/tPSA by 6.4%. Subsequent storage of serum at 4 degrees C for 1 week resulted in a 25% decrease from the baseline value. After 1 month at -20 degrees C the fPSA value was 13% lower than the baseline value.

CONCLUSION

These results indicate that if there is to be confidence in the accuracy of the f/tPSA value, then blood samples must be handled and processed correctly. Total PSA is sufficiently stable to permit whole blood samples to remain at room temperature for 24 h before serum is separated. If fPSA is to be determined accurately then the whole blood sample must be centrifuged promptly. As the fPSA values in blood samples left at room temperature for 24 h are up to 25% lower than those on immediate assay, and the subsequent f/tPSA 29% lower, then for the optimum use of this test, these samples should also be handled appropriately.

The Combination of Human Glandular Kallikrein and Free Prostate-specific Antigen (PSA) Enhances Discrimination Between Prostate Cancer and Benign Prostatic Hyperplasia in Patients with Moderately Increased Total PSA

Background: Prostate-specific antigen (PSA) is the most reliable tumor marker available and is widely used for the diagnosis and management of prostate cancer. Unfortunately, PSA cannot distinguish efficiently between benign and malignant disease of the prostate, especially within the range of 4–10 μg/L. Among the refinements developed to enhance PSA specificity is the free/total PSA ratio, which is useful in discriminating between the two diseases within the diagnostic “gray zone”. Recent data indicate that human glandular kallikrein (hK2), a protein with high homology to PSA, may be an additional serum marker for the diagnosis and monitoring of prostate cancer.

Methods: We analyzed 206 serum samples (all before treatment was initiated) from men with histologically confirmed benign prostatic hyperplasia (n = 100) or prostatic carcinoma (n = 106) with total PSA in the range of 2.5–10 μg/L. Total and free PSA and hK2 were measured with noncompetitive immunological procedures. Statistical analysis was performed to investigate the potential utility of the various markers or their combinations in discriminating between benign prostatic hyperplasia and prostatic carcinoma.

Results: hK2 concentrations were not statistically different between the two groups of patients. There was a strong positive correlation between hK2 and free PSA in the whole patient population. hK2/free PSA ratio (area under the curve = 0.69) was stronger predictor of prostate cancer than the free/total PSA ratio (area under the curve = 0.64). At 95% specificity, the hK2/free PSA ratio identified 30% of patients with total PSA between 2.5–10 μg/L who had cancer. At 95% specificity, the hK2/free PSA ratio identified 25% of patients with total PSA between 2.5 and 4.5 μg/L who had cancer.

Conclusions: Our data suggest that hK2 in combination with free and total PSA can enhance the biochemical detection of prostate cancer in patients with moderately increased total PSA concentrations. More specifically, the hK2/free PSA ratio appears to be valuable in identifying a subset of patients with total PSA between 2.5 and 4.5 μg/L who have high probability of cancer and who should be considered for biopsy.

Use of human glandular kallikrein 2 for the detection of prostate cancer: preliminary analysis

OBJECTIVES

Human glandular kallikrein 2 (hK2) and prostate-specific antigen (PSA) are members of a multigene family of serine proteases that share approximately 80% sequence homology. Both are expressed in the prostate epithelium, are under androgen regulation, are present in serum and seminal fluid, and can form complexes with endogenous protease inhibitors (eg, alpha2-macroglobulin and alpha1-antichymotrypsin). Differences in immunohistochemistry and substrate specificity suggest hK2 may provide unique information for early detection and characterization of prostate cancer.

METHODS

Nine hundred thirty-seven archived serum samples from men treated at two academic institutions were studied. All men underwent biopsy, had a histologically confirmed diagnosis of cancer or noncancer, and a total PSA level greater than 2 ng/mL. Samples were tested in Hybritech's Tandem-R PSA and Tandem-R free PSA (fPSA) assays and a research prototype assay for total hK2 (thK2).

RESULTS

The thK2/fPSA ratio provided additional specificity for cancer detection over PSA and the percentage of fPSA (%fPSA). A model for cancer detection using %fPSA and the thK2/fPSA ratio when PSA is 2 to 4 ng/mL is proposed that would identify as many as 40% of the cancers and would require biopsy in only 16.5% of the men in this PSA range.

CONCLUSIONS

In this study, %fPSA and thK2/fPSA provided unique information for prostate cancer detection and increased the specificity of cancer detection.

Prostate cancer

Prostate cancer is the second leading cause of cancer death in men. Recommendations for screening and treatment are usually made, especially in the popular press, without regard to patient age or medical health. This article focuses on the trade-off between the benefits and side effects of screening and treatment.

Prostate-specific antigen adjusted for the transition zone volume versus free-to-total prostate-specific antigen ratio in predicting prostate cancer

BACKGROUND

We performed this study to assess the efficacy of prostate-specific antigen adjusted for the transition zone volume (PSATZ) and free-to-total prostate-specific antigen (PSA) ratio (F/T ratio) in predicting prostate cancer in men with intermediate PSA levels of 4.1-10.0 ng/mL.

METHODS

Between March 1997 and September 1998, PSATZ was obtained from 67 patients who underwent ultrasonography guided systemic sextant biopsies and had a PSA of 4.1-10.0 ng/mL. PSATZ was compared with F/T ratio via receiver operating characteristic (ROC) curves.

RESULTS

Of 67 patients, 22 (32.8%) had prostate cancer and 45 (67.2%) had benign prostatic hyperplasia (BPH) on pathologic examination. Mean PSA, PSA density, F/T ratio and PSATZ were 7.96+/-2.01ng/mL, 0.28+/-0.14 ng/mL/cc, 0.10+/-0.06 and 0.70+/-0.28 ng/mL/cc in patients with prostate cancer and 6.39+/-1.68 ng/mL, 0.16+/-0.06 ng/mL/cc, 0.15+/-0.05 and 0.29+/-0.10 ng/mL/cc in patients with BPH, respectively. The ROC curve analysis demonstrated that PSATZ predicted the biopsy outcome significantly better than F/T ratio in all 67 patients (P<0.01) and in a subset of 53 men with normal digital rectal examination (P<0.01). With a cut-off value of 0.35 ng/mL/cc, PSATZ had a sensitivity of 86% and a specificity of 89% for predicting prostate cancer.

CONCLUSIONS

These results suggest that PSATZ and F/T ratio may be useful in diagnosing prostate cancer with intermediate levels of PSA. Prostate-specific antigen adjusted for the transition zone volume is more accurate than F/T ratio in distinguishing benign prostatic disease from prostate cancer. But large prospective studies are required to assess the precise role of PSATZ and F/T ratio in early prostate cancer detection.

The necessity of a second prostate biopsy cannot be predicted by PSA or PSA derivatives (density or free:total ratio) in men with prior negative prostatic biopsies

Serum prostate specific antigen, prostate specific antigen density and free:total prostate specific antigen are known to be useful for determining the risk of prostate cancer in patients undergoing prostate cancer screening. The patient with a positive biopsy presents no future prostate specific antigen dilemma. Those with negative biopsies often go on to numerous repeat biopsies. Our goal was to establish criteria that could be used to identify patients who will require repeat prostate biopsies (possibly false negative initial biopsy), while not exposing the low risk population (probable true negative initial biopsy) to additional invasive procedures. Between March 1991 and March 1998, 148 patients who had a biopsy for an elevated prostate specific antigen value (4.1-10.0) or an altered digital rectal examination, had no cancer found in the specimen. From these, 51 (34.4%) had repeated biopsies, while the others persisted on close follow-up. We examined their serum prostate specific antigen, prostate specific antigen density and free:total prostate specific antigen value, as well as their age and histology results of the initial and repeat biopsy, to determine if any predictor of the need for a repeat biopsy could be identified. Eight (15.7%) from 51 men who had repeat biopsy had prostate cancer detected. Forty three (84.3%) patients persisted with a negative biopsy, despite filling the criteria for re-biopsy. Multivariate analysis failed to identify any significant predictors of prostate cancer in the repeat biopsy group. Despite initial success, the prostate specific antigen derivatives and free:total prostate specific antigen have not safely limited the number of biopsies performed for an abnormal prostate specific antigen (4.1-10.0). Neither prostate specific antigen density nor free:total prostate specific antigen predicted the need for repeat biopsy in this specific group. The results of this ongoing study demonstrate that to date, prostate specific antigen and prostate specific antigen derivatives can not be utilized to determine which patients will be at high risk for requiring repeat prostate biopsy. All patients must be closely monitored for evidence of a change in status from benign to malignant disease, and new markers for this purpose are urgently needed.

Prostate specific antigen: a decade of discovery--what we have learned and where we are going

PURPOSE

Many advances have occurred during the last decade in the clinical use of prostate specific antigen (PSA) for detecting, staging and monitoring prostate cancer. We review the clinical usefulness and limitations of serum PSA as a tumor marker of prostate cancer.

MATERIALS AND METHODS

The English language literature was reviewed with respect to the major contributions and limitations of PSA in present clinical practice.

RESULTS

Although controversial, age specific PSA reference ranges can improve the sensitivity for prostate cancer detection in young men and the specificity in older men. Percent free PSA improves the specificity for prostate cancer detection in men with PSA values between 4 and 10 ng./ml., and a PSA density of greater than 0.15 may better distinguish benign prostatic hyperplasia from prostate cancer. PSA velocity can improve the ability to detect prostate cancer when 3 serial PSA values are measured during a 2-year period. For prostate cancer staging PSA is most useful combined with clinical stage and Gleason score in multivariate analysis. Percent free PSA may prove useful for staging prostate cancer but further clinical trials are needed to determine its clinical usefulness. PSA is the most clinically useful means to monitor disease recurrence after treatment of prostate cancer. With ultrasensitive PSA assays it is now possible to increase the lead time for detection of disease recurrence by several months.

CONCLUSIONS

During the last decade much of the focus has been on improving the ability of this tumor marker to detect prostate cancer. PSA remains the best and most widely used tumor marker in urology today.

Estimation of Prostate Cancer Probability by Logistic Regression: Free and Total Prostate-specific Antigen, Digital Rectal Examination, and Heredity Are Significant Variables

Background: Despite low specificity, serum prostate-specific antigen (PSA) is widely used in screening for prostate cancer. Specificity can be improved by measuring free and total PSA and by combining these results with clinical findings. Methods such as neural networks and logistic regression are alternatives to multistep algorithms for clinical use of the combined findings.

Methods: We compared multilayer perceptron (MLP) and logistic regression (LR) analysis for predicting prostate cancer in a screening population of 974 men, ages 55–66 years. The study sample comprised men with PSA values &gt;3 μg/L. Explanatory variables considered were age, free and total PSA and their ratio, digital rectal examination (DRE), transrectal ultrasonography, and a family history of prostate cancer.

Results: When at least 90% sensitivity in the training sets was required, the mean sensitivity and specificity obtained were 87% and 41% with LR and 85% and 26% with MLP, respectively. The cancer specificity of an LR model comprising the proportion of free to total PSA, DRE, and heredity as explanatory variables was significantly better than that of total PSA and the proportion of free to total PSA (P &lt;0.01, McNemar test). The proportion of free to total PSA, DRE, and heredity were used to prepare cancer probability curves.

Conclusion: The probability calculated by logistic regression provides better diagnostic accuracy for prostate cancer than the presently used multistep algorithms for estimation of the need to perform biopsy.

Comparative study of assays for prostate-specific antigen molecular forms

BACKGROUND

The detection of prostate-specific antigen (PSA) molecular forms such as free PSA and PSA-ACT and the use of PSA molecular ratios, especially the percentage of free to total PSA, have been reported to improve the diagnostic accuracy of prostate cancer in the patients with slightly elevated serum PSA values. However, the correlation among the values of serum free PSA or PSA-ACT obtained in various assays remains unclear.

METHODS

Serum free PSA and PSA-ACT values were detected with the following assays: Hybritech, DPC, EIKEN, Abbott, Roche and Can-Ag for free PSA and Dainippon, Chugai, EIKEN and Bayer for PSA-ACT. The data obtained with each assay were compared with Hybritech (free PSA) and Dainippon (PSA-ACT) as standards.

RESULTS

The free PSA data obtained with the Hybritech, EIKEN, Abbott and Can-Ag kits were similar. The values obtained with the DPC and Roche kits showed a linear regression of y = ax + b with those obtained with the Hybritech, with a b value of zero and an a value of 1.20 and 1.57, respectively. The serum PSA-ACT values detected with the Dainippon and Chugai kits were identical. The equation for converting the data obtained with the EIKEN kits to the Dainippon value was 0.7636 x (EIKEN) + 0.1381.

CONCLUSIONS

Serum free PSA and PSA-ACT values obtained with various assays were not necessarily the same. Some kits for the assay of free PSA and PSA-ACT gave the same serum values. The free PSA values obtained with the other kits could be converted using appropriate equations. The gamma-Sm values showed wide variations and were not considered suitable as a measurement of free PSA.