Free and complexed prostate-specific antigen serum ratios to predict probability of primary prostate cancer and benign prostatic hyperplasia

Five-Year Stability Study of Free and Total Prostate-Specific Antigen Concentrations in Serum Specimens Collected and Stored at – 70°C or Less

The stability of total (t) and free (f) prostate-specific antigen (PSA) in male serum specimens stored at –70°C or lower temperature for 4.7 to 4.9 years was studied. Until now, the stability of these analytes in serum has not been evaluated systematically beyond 2 years of storage at –70°C. Aliquots of frozen serum were thawed in 2001 and 2006 and assayed for tPSA and fPSA using a Dade Behring Dimension(r) RxL analyzer and reagents. tPSA values ranged from 0.07 to 69.94 and 0.00 to 69.83 ng/mL in 2001 and 2006, respectively, whereas fPSA values for the tested specimens ranged from 0.02 to 5.72 and 0.00 to 5.92, respectively. Deming regression analyses showed agreement in assay values over time as tPSA values yielded a slope of 1.0112 and a y-intercept of 0.0195; fPSA values produced a slope 1.0538 and a y-intercept of –0.0442; f/tPSA values yielded a slope of 0.9631 and a y-intercept of 0.1195. A Bland-Altman analysis of the data demonstrated analyte and ratio stability over this time period. We conclude that serum, when collected properly and stored at –70°C or lower temperature, may be used for tPSA and fPSA clinical studies for at least 5 years after collection.

Neuro-fuzzy system for prostate cancer diagnosis

OBJECTIVES

To develop a neuro-fuzzy system to predict the presence of prostate cancer. Neuro-fuzzy systems harness the power of two paradigms: fuzzy logic and artificial neural networks. We compared the predictive accuracy of our neuro-fuzzy system with that obtained by total prostate-specific antigen (tPSA) and percent free PSA (%fPSA).

METHODS

The data from 1030 men (both outpatients and hospitalized patients) were used. All men had a tPSA level of less than 20 ng/mL. Of the 1030 men, 195 (18.9%) had prostate cancer. A neuro-fuzzy system was developed using the coactive neuro-fuzzy inference system model.

RESULTS

The mean area under the receiver operating characteristic curve for the neuro-fuzzy system output was 0.799 +/- 0.029 (95% confidence interval 0.760 to 0.835), for tPSA, it was 0.724 +/- 0.032 (95% confidence interval 0.681 to 0.765), and for %fPSA, 0.766 +/- 0.024 (95% confidence interval 0.725 to 0.804). Furthermore, pairwise comparison of the area under the curves evidenced differences among %fPSA, tPSA, and neuro-fuzzy system's output (tPSA versus neuro-fuzzy system's output, P = 0.008; %fPSA versus neuro-fuzzy system's output, P = 0.032). The comparison at 95% sensitivity showed that the neuro-fuzzy system had the best specificity (31.9%).

CONCLUSIONS

This study presented a neuro-fuzzy system based on both serum data (tPSA and %fPSA) and clinical data (age) to enhance the performance of tPSA to discriminate prostate cancer. The predictive accuracy of the neuro-fuzzy system was superior to that of tPSA and %fPSA.

Case-control and two-gate designs in diagnostic accuracy studies

BACKGROUND

In some diagnostic accuracy studies, the test results of a series of patients with an established diagnosis are compared with those of a control group. Such case-control designs are intuitively appealing, but they have also been criticized for leading to inflated estimates of accuracy.

METHODS

We discuss similarities and differences between diagnostic and etiologic case-control studies, as well as the mechanisms that can lead to variation in estimates of diagnostic accuracy in studies with separate sampling schemes ("gates") for diseased (cases) and nondiseased individuals (controls).

RESULTS

Diagnostic accuracy studies are cross-sectional and descriptive in nature. Etiologic case-control studies aim to quantify the effect of potential causal exposures on disease occurrence, which inherently involves a time window between exposure and disease occurrence. Researchers and readers should be aware of spectrum effects in diagnostic case-control studies as a result of the restricted sampling of cases and/or controls, which can lead to changes in estimates of diagnostic accuracy. These spectrum effects may be advantageous in the early investigation of a new diagnostic test, but for an overall evaluation of the clinical performance of a test, case-control studies should closely mimic cross-sectional diagnostic studies.

CONCLUSIONS

As the accuracy of a test is likely to vary across subgroups of patients, researchers and clinicians might carefully consider the potential for spectrum effects in all designs and analyses, particularly in diagnostic accuracy studies with differential sampling schemes for diseased (cases) and nondiseased individuals (controls).

Evolution of free, complexed, and total serum prostate-specific antigen and their ratios during 1 year of follow-up of men with febrile urinary tract infection

OBJECTIVES

To determine the serum values of free, complexed, and total prostate-specific antigen (PSA) and their ratios in men with febrile urinary tract infection (UTI) during 1 year of follow-up.

METHODS

A total of 54 men were prospectively enrolled in the study, and serum samples were obtained at the acute stage of the UTI and after 1, 3, 6, and 12 months.

RESULTS

Most men had a rise (median 3.1, 7.2, and 14.1 ng/mL, respectively) in free PSA (fPSA), complexed PSA (cPSA), and total PSA (tPSA) during the acute phase of the UTI. After 1 month, fPSA rapidly decreased to levels that were maintained during the rest of the follow-up period, and cPSA and tPSA declined more slowly. At 1, 3, and 6 months after the infection the fPSA/tPSA and fPSA/cPSA ratios were abnormal in one half to two thirds of the men (median ratio 11%, 15%, and 16% and 17%, 24%, and 24%, respectively), comparable to findings in patients with prostate cancer.

CONCLUSIONS

These results confirmed that the prostate is involved in men with febrile UTI. The low fPSA/tPSA and fPSA/cPSA ratios in combination with sustained elevations of cPSA and tPSA for up to 6 months after UTI could be falsely interpreted as a sign of prostate cancer. The prolonged elevation of cPSA indicates a long-lasting inflammation of the nonadenomatous parts of the prostate.

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 <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 >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.

Contemporary use of complexed PSA and calculated percent free PSA for early detection of prostate cancer: impact of changing disease demographics

OBJECTIVES

To assess the diagnostic performance of complexed prostate-specific antigen (cPSA), total PSA (tPSA), and calculated free/total PSA (f/t PSA) ratios in the differentiation of benign disease from prostate cancer (CaP) using a contemporary patient cohort.

METHODS

The cPSA, tPSA, and calculated fPSA values were determined using the Bayer Immuno-1 system. To validate our calculated f/t PSA ratio, we also retrospectively measured fPSA using the Abbott AxSYM immunoassay system in archival pretreatment sera obtained between 1990 and 1997 from 362 men with clinically and biopsy-confirmed benign prostatic hyperplasia (n = 179) or CaP (n = 183). The diagnostic utility of tPSA, cPSA, and the calculated f/t PSA ratio was assessed using a contemporary test population consisting of sera prospectively collected between June 1999 and June 2000 from 3006 men who had recently undergone a systematic biopsy by urologists in clinical practices throughout the United States. This contemporary patient sample had biopsy diagnoses of either no evidence of malignancy (n = 1857) or CaP (n = 1149). All serum samples had tPSA values between 2.0 and 20.0 ng/mL.

RESULTS

The measured versus calculated f/t PSA ratios had a Pearson's correlation coefficient of 0.9130 in the retrospectively studied population of 362 men. The areas under the receiver operating characteristic curves (ROC-AUCs) for the measured and calculated f/t PSA ratios were indistinguishable (69.6% versus 69.2%, respectively). In the contemporary population (n = 3006), the ROC-AUC for tPSA, cPSA, and the calculated f/t PSA ratio was 52.2%, 53.9%, and 58.4%, respectively. We also compared the diagnostic performance using published cutoffs for tPSA (greater than 4.0 ng/mL), cPSA (greater than 3.8 ng/mL), and the f/t PSA ratio (greater than 15% and greater than 25%) in tPSA reflex ranges of 2 to 20 ng/mL and 2 to 10 ng/mL. We found that both cPSA and the f/t PSA ratio (greater than 25% cutoff) outperformed tPSA and yielded similar results in terms of biopsies spared and cancers missed.

CONCLUSIONS

The calculated f/t PSA ratio and cPSA perform equally well in terms of the improvement of specificity in the discrimination of benign disease and CaP. The f/t PSA ratio and cPSA provide clinical benefits over the use of tPSA alone, such as an increased sparing of unnecessary biopsies performed with a manageable degree of risk of delayed cancer detection.

[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.

Free and complexed prostate-specific antigen (PSA) in the early detection of prostate cancer

We evaluated the analytical performance and diagnostic utility of complexed prostate-specific antigen (CPSA) and their ratios, complexed-to-total PSA (C/T PSA) and free-to-complexed PSA (F/C PSA), in comparison with the total PSA (TPSA) and free-to-total PSA ratio (F/T PSA) as means of diagnosing prostate cancer (PC). Samples (n=101) were drawn from men with no evidence of malignancy (n=80) and from men with PC (n=21) at biopsy. For determination of the F/T PSA ratio, the DPC Immulite-2000 method was used; and the Bayer Immuno-1 CPSA and TPSA assays were used to determine the C/T PSA ratio. The Bayer Immuno-1 CPSA assay provides accurate and precise CPSA values in human serum. The performance of the different forms and ratios was compared using receiver operating characteristic curve analysis. CPSA had the greatest area under the curve (AUC, 0.689) although it was not statistically different from the other parameters. A cut-off value of 4.66 ng/ml for CPSA provided a specificity of 38% and a sensitivity of 93%. The F/C PSA ratio maintained a sensitivity of 93% and had an increased specificity of 41%. The measurement of CPSA provides a slight increase in specificity compared with the use of the TPSA in the early detection of prostate cancer.

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.

Predicting the outcome of prostate biopsy in screen-positive men by a multilayer perceptron network

OBJECTIVES

To assess whether an artificial neural network (multilayer perceptron, MLP) and logistic regression (LR) could eliminate more false-positive prostate-specific antigen (PSA) results than the proportion of free PSA in a prostate cancer screening.

METHODS

MLP and LR models were constructed on the basis of data on total PSA, the proportion of free PSA, digital rectal examination (DRE), and prostate volume from 656 consecutive men (aged 55 to 67 years) with total serum PSA concentrations of 4 to 10 ng/mL in the randomized population-based prostate cancer screening study in Finland. The MLP and LR models were validated using the "leave-one-out" method.

RESULTS

Of the 656 men, 23% had prostate cancer and 77% had either normal prostatic histology or a benign disease. At a 95% sensitivity level, 19% of the false-positive PSA results could be eliminated by using the proportion of free PSA versus 24% with the LR model and 33% with the MLP model (P < 0.001). At 80% to 99% sensitivity levels, the accuracy of the MLP and LR models was significantly higher than that of the proportion of free PSA. At 89% to 99% sensitivities, the accuracy of the MLP was higher than that of LR (P </= 0.001).

CONCLUSIONS

At clinically relevant sensitivity levels, the MLP and LR models based on total PSA, the proportion of free PSA, DRE, and prostate volume could reduce the number of unnecessary biopsies significantly better than the proportion of free PSA alone in men with total PSA levels in the range 4 to 10 ng/mL.

Probability of prostate cancer detection based on results of a multicenter study using the AxSYM free PSA and total PSA assays

OBJECTIVES

The determination of the percentage of free prostate-specific antigen (%fPSA) enhances the specificity of prostate cancer (CaP) detection. This study was undertaken to assess the performance of %fPSA in differentiating benign prostate disease from CaP and to determine the CaP probability estimates using the AxSYM Free PSA and AxSYM Total PSA assays.

METHODS

In this prospective study, 297 men, 50 years old or older, with a total PSA level between 4 and 10 ng/mL and a nonsuspicious digital rectal examination were enrolled at 10 clinical sites. All subjects underwent at least sextant prostate biopsies to establish the diagnosis. fPSA and total PSA (tPSA) levels were determined using the AxSYM Free PSA and AxSYM Total PSA assays. Percent fPSA values were compared with tPSA values to determine the appropriate cutoffs for prostate biopsy and to calculate the CaP probability estimates.

RESULTS

The strongest predictor of CaP in a logistic regression model was %fPSA (odds ratio 2.29), which contributed significantly more than age or tPSA to the predictive model. In this study population, a %fPSA cutoff of 26.4% would have detected 96% of subjects with CaP (sensitivity) and would have eliminated 27.4% of unnecessary biopsies (specificity). CaP probability estimates ranged from 9% to 69% and increased as the %fPSA value decreased. Men with a %fPSA level of 10% or lower had a 69% probability of CaP, and men with a %fPSA level of greater than 26% had a 9% probability of CaP.

CONCLUSIONS

Percent fPSA values can help differentiate CaP from benign prostate disease and reduce unnecessary biopsies in 27% of men 50 years old or older whose digital rectal examination was normal and whose tPSA level was between 4 and 10 ng/mL. A %fPSA result can assist the physician and patient in determining the probability of CaP and assessing the need for prostate biopsy.

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.

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.

Free/total PSA ratio improves differentiation of benign and malignant disease of the prostate: critical analysis of two different test populations

OBJECTIVES

To evaluate the ability of free PSA (fPSA), total PSA (tPSA), and the free/total PSA (f/t PSA) ratio to differentiate between benign prostate disease (benign prostatic hyperplasia [BPH] and no evidence of malignancy [NEM]) and prostate cancer (CaP) using two different testing populations, and to compare predictive probabilities for the two test populations.

METHODS

One test population consisted of sera from 531 men with clinically well-defined and biopsy-confirmed BPH (n = 255) or CaP (n = 276), with tPSA values ranging from 2 to 20 ng/mL. All of these serum samples were retrospective and obtained from patients evaluated in academic settings before any treatment. A second test population consisted of a prospective analysis of sera obtained from 4870 men, collected by urologists throughout the United States and processed at a single pathology laboratory. All these patients had a systematic biopsy evaluated and diagnosed at the same pathology laboratory, with the diagnosis categorized as either NEM (n = 2961) or CaP (n = 1909). No additional information on concurrent disease or pre- or current treatment status was known for this test population. For both populations, two tPSA reflex range groups, 2 to 10 and 2 to 20 ng/mL, were evaluated.

RESULTS

Both test populations benefited from the application of either fPSA alone or the f/t PSA ratio to differentiate benign from malignant disease (t test P value less than 0.001). The receiver operating characteristic (ROC) curve for the f/t PSA ratio had an area under the curve (AUC) of 72% for n = 531 versus 63% for n = 4870, irrespective of the tPSA reflex range. Average fPSA values demonstrated a linear correlation to a range of tPSA concentrations for both test populations. Predictive probabilities (adjusted for established cancer prevalence rates in the academic population [n = 531]) calculated using f/t PSA ratios also demonstrated their value in contrasting the performance characteristics in the two test populations.

CONCLUSIONS

The fPSA and f/t PSA ratio improved the differentiation of benign disease and CaP in two different patient samples. The f/t PSA ratio demonstrated an increased sensitivity and specificity when applied to differentiate clinically well-defined BPH and CaP (n = 531). The differences in the results between the two test samples are probably attributable to the variability of the patient's disease and treatment status in the larger, less refined, community-based population. The use of predictive probabilities provides the opportunity to provide patient-specific cancer probabilities instead of using population-based specific single cutoffs.

Prostate-specific antigen

Prostate specific antigen (PSA) is serine protease produced at high concentrations by normal and malignant prostatic epithelium. It is mainly secreted into seminal fluid, where it digests the gel forming after ejaculation. Only minor amounts of PSA leak out into circulation from the normal prostate, but the release of PSA is increased in prostatic disease. Thus PSA is a sensitive serum marker for prostate cancer but its specificity is limited by a high frequency of falsely elevated values in men with benign prostatic hyperplasia (BPH). Approximately two-thirds of all elevated values (>4 microg/l) in men over 50 years of age are due to BPH. In serum, most of the PSA immunoreactivity consists of a complex between PSA and alpha1-antichymotrypsin (PSA-ACT) whereas approximately 5-40% are free. The proportion of PSA-ACT is larger and the free fraction is smaller in prostate cancer than in benign prostatic hyperplasia (BPH). Determination of the proportion of free PSA has become widely used to improve the cancer specificity of PSA especially in men with PSA values in the 'grey zone' (4-10 microg/l). PSA also occurs in complexes with other protease inhibitors and determination of these and other markers may further improve the diagnostic accuracy for prostate cancer. Interpretation of the results for many different markers is complicated, but this can be simplified by using statistical methods. The diagnostic accuracy can be further improved by using logistic regression or neural networks to estimate the combined impact of marker results and other findings like digital rectal examination (DRE), transrectal ultrasound (TRUS) and heredity.

Interleukin-8 serum levels in patients with benign prostatic hyperplasia and prostate cancer

OBJECTIVES

Using arbitrarily primed polymerase chain reaction (AP-PCR) ribonucleic acid (RNA) fingerprinting, we discovered a messenger RNA (mRNA) that encoded the cytokine interleukin-8 (IL-8) that was up-regulated in the peripheral blood leukocytes (PBLs) of patients with metastatic prostate cancer (CaP) compared with similar cells from healthy individuals. We compared the total prostate-specific antigen (PSA) levels, the free/total (f/t) PSA ratios, and the immunoreactive IL-8 serum concentrations in patients with either biopsy-confirmed benign prostatic hyperplasia (BPH) or CaP.

METHODS

The sera from 35 apparently healthy normal volunteers and 146 patients with biopsy-confirmed BPH and CaP obtained from two academic centers were retrospectively examined to determine the serum levels of IL-8, total PSA (tPSA), and the f/t PSA ratio. Logistic regression and trend analysis statistical methods were used to assess the results.

RESULTS

Normals (n = 35), BPH patients (n = 53), patients with clinical Stages A to C CaP (n = 81), and patients with metastatic CaP (n = 1 2) had mean levels of IL-8 of 6.8, 6.5, 15.6, and 27.8 pg/mL, respectively. The IL-8 serum concentrations correlated with increasing CaP stage and also differentiated BPH from clinical Stages A, B, C, or D CaP better than tPSA and performed similarly to the f/t PSA ratio. The combination of the IL-8 levels and f/t PSA ratios using multivariate logistic regression analysis distinguished BPH from Stages A, B, C, or D CaP or only Stages A and B with a receiver operating characteristic area under the curve of 89.8% and 87.5%, respectively (P <0.0001).

CONCLUSIONS

The IL-8 serum concentration in our clinically well-defined patient sample was independent of the f/t PSA ratio as a predictor of CaP. When test samples are controlled for extraneous clinical origin of inflammation or infection, the combination of the IL-8 and f/t PSA assay results may offer an improved approach for distinguishing BPH from CaP.

The clinical importance of free prostate‐specific antigen (PSA)

The proportion of free prostate-specific antigen (PSA) in serum relative to total PSA (F/T) is lower in patients with prostate cancer than in those with elevated levels of PSA due to benign prostatic disease. When applied to early diagnosis and screening for prostate cancer, the proportion of free PSA can be used to reduce the number of false-positive results by 20-40%. The utility of F/T is better in men with a small prostate volume, i.e. in relatively young men, who are most likely to benefit from early diagnosis and treatment of prostate cancer. The concentrations of PSA and especially free PSA are affected by considerable intra-individual variation and sample stability. Assay standardization is variable and it is therefore important to establish reference values for the methods used. Better control of these factors is likely to improve the diagnostic accuracy. The utility of determining free PSA can be improved by evaluating the combined impact of free and total PSA by logistic regression analysis or neural networks.

Free/total prostate-specific antigen ratio can prevent unnecessary prostate biopsies

OBJECTIVES

To evaluate the ability of free/total prostate-specific antigen (PSA) ratio to improve specificity of prostate cancer detection, compare Diagnostic Products Corporation (DPC) Immulite and Ciba Corning ACS 180 total (t)PSA assay, and define an assay-specific cutoff point and reflex range for DPC PSA ratio (PSAR).

METHODS

In a prospective study, 206 men were enrolled with measurement of both assays. Group 1 consisted of 173 men with a suspicion of prostate cancer (PCA). Thirteen men with known PCA (group 2) and 20 men younger than 32 years (group 3) were used as control groups.

RESULTS

Our results in group 1 (115 with benign prostatic hyperplasia [BPH], 58 with PCA) revealed a sensitivity of 82.7%, a specificity of 45.2%, and an accuracy of 57.8% for the DPC tPSA assay (cutoff point more than 4.0 ng/mL) within the entire PSA range. tPSA values of the ACS 180 assay were 1.97-fold higher. Within the tPSA gray zone of 2.5 to 10 ng/mL (66 BPH, 23 PCA), specificity and accuracy of DPC tPSA can be improved by using the DPC PSAR (cutoff point less than 19%) from 33.3% to 71.2% and 42.7% to 70.8%, respectively, maintaining the same sensitivity level of 69.6%.

CONCLUSIONS

By combining tPSA testing with PSAR within the gray zone, 39.7% (25 of 63) of unnecessary biopsies can be saved, without missing any additional cancers compared with tPSA testing alone. The optimal reflex range for DPC PSAR is 2.5 to 10 ng/mL and the best PSAR cutoff point for biopsy criterion is less than 19% in our high-risk population, with a cancer yield of 34%. Because we still do not have an international PSA standard, it is important to use assay-specific "normal values" and PSAR cutoff points.

Human Kallikrein 2 (hK2) and prostate-specific antigen (PSA): two closely related, but distinct, kallikreins in the prostate

Recent studies on human kallikrein 2 (hK2) have revealed striking similarities and significant differences with the closely related kallikrein PSA. Both PSA and hK2 are primarily localized to the prostate and share close structural similarities. Although both kallikreins are produced by the same secretory epithelial cells in the prostate, hK2 is associated more with prostate tumors than PSA and is highly expressed in poorly differentiated cancer cells. The potent trypsin-like activity of hK2 contrasts with the weak chymotrypsin-like activity of PSA. The inactive precursor form of PSA, proPSA, is converted rapidly to active PSA by hK2, suggesting an important in vivo regulatory function by hK2 on PSA activity. The high homology between hK2 and PSA results in significant cross-reactivity to hK2 by polyclonal and some monoclonal antibodies to PSA. Future studies on both PSA and hK2 need to take into account this potential for cross-reactivity. Specific monoclonal antibodies to hK2 have now demonstrated that serum levels of hK2, like PSA, are correlated with prostate cancer. The production of hK2 protein in active protease form and specific monoclonal antibodies to the hK2 antigen will allow extensive future studies delineating the physiological and clinical utility of this new prostate antigen.

Percent free prostate-specific antigen after radiotherapy for prostate cancer

OBJECTIVES

The range of "normal" prostate-specific antigen (PSA) values compatible with cure following radiotherapy (RT) for prostate cancer (PCa) has yet to be established. Various thresholds, ranging from 0.5 to 4.0 ng/mL are used to define biochemical disease-free status. Because the proportion of free PSA is lower in men with PCa, the ratio of free PSA to total PSA could theoretically be useful in determining cancer-free status after RT.

METHODS

One hundred two men treated with standard external beam RT from October 1988 to October 1994 (median dose, 66 Gy) were chosen for measurement of percent free PSA because they had a routine follow-up visit in November or December of 1996. All patients had undergone systematic transrectal ultrasound-guided biopsies after RT. Biopsies were negative in 66 patients, positive in 21, and indeterminate in 15 (rare, degenerated cancer cells with no evidence of proliferation by immunohistochemical stains). Stage distribution was T1b, 8; T1c, 9; T2a, 25; T2b/c, 40; and T3, 20. Median follow-up is 40 months.

RESULTS

Total serum PSA ranged from 0. 1 to 10.0 ng/mL. Because the mean (+/-SD) percent free PSA for patients with negative (n = 66) and indeterminate (n = 15) biopsies were 29% +/- 18% and 25% +/- 7%, respectively (P = 0.13), these were combined. The mean (+/-SD) percent free PSA for those with positive biopsies (n = 21) was 15% +/- 8% and was significantly different from those with negative or indeterminate biopsies (P < 0.001). Patients with negative or indeterminate biopsies were grouped according to their total PSA as 0.1 to 0.5 ng/mL (n = 33), 0.6 to 1.0 ng/mL (n = 23), 1.1 to 2.0 ng/mL (n = 17), and greater than 2.0 ng/mL (n = 7). The mean percent free PSAs were 34%, 28%, 21%, and 12%, respectively.

CONCLUSIONS

Percent free PSA may be a useful adjunct in diagnosing recurrent PCa after RT. The ratio is significantly different in patients of known biopsy status, distinguishing a group with positive biopsies from those with negative. However, there is overlap in individual values, and because patients with negative biopsies after RT may have subclinical distant disease, more follow-up is necessary before percent free PSA can be incorporated into a definition of biochemical disease-free status. Percent free PSA may be most useful for PSA from 0.6 to 2.0 ng/mL, where failure is common, but not universal.

The utility of free to total PSA ratio for detecting prostate cancer in Japanese men with total PSA between 2.1 and 10 ng/ml

We sought to determine whether the free to total prostate specific antigen (PSA) ratio in men with "gray zone" total PSA could accurately indicate the presence or absence of cancer, thus reducing the number of unnecessary biopsies without lessening the chance of detecting early stage prostate cancers. In 137 patients with total PSA levels between 2.1 and 10.0 ng/ml, we examined total PSA, free to total PSA ratio, PSA density (PSAD), and prostatic volume measured by transrectal ultrasound, and used these features to predict histologic features determined following sextant biopsy and/or surgery of the prostate. Of 137 patients with intermediate PSA levels, 25 (18%) had cancer. With a free to total PSA cut-off of 20%, cancer would not have been detected in 4 of the 25 patients (84% sensitivity), and 36% of the unnecessary negative biopsies would have been successfully avoided (p < 0.0005). With a PSAD cut-off of 0.15, cancer would have been missed in 4 of the 25 patients (84% sensitivity) and a 50% reduction in unnecessary negative biopsies would have been possible (p < 0.0005). Of 41 patients with large prostatic glands (>40 cm(3)), cancer was detected in only one, compared with 24 (25%) of 96 patients with small glands (<40 cm(3)) (p = 0.002). The results of receiver operating characteristic analysis indicated that PSAD, free to total PSA ratio, and prostatic volume would be effectively applicable to the diagnosis of cancer (areas under the curve: 0.7562, 0.7564, and 0.7693, respectively). At 100% sensitivity, specificity was highest for PSAD used in conjunction with ratio of free to total PSA. All patients with cancer had PSAD > 0.15 and/or free to total PSA < 15%. Patients with PSAD < 0.15 and free to total PSA ratio > 15% had no cancer (p < 0.0001). By this procedure, a 48% (54 of 112) reduction in the number of unnecessary biopsies would have been possible. Use of the free to total PSA ratio, measured with the AxSYM system, can significantly reduce unnecessary negative biopsies in patients with intermediate levels of PSA. Prostatic volume data can enhance the usefulness of this ratio for diagnosing prostate cancer.