Multicenter comparison of the diagnostic performance of free prostate-specific antigen

Capillary electrophoresis of urinary prostate glycoproteins assists in the diagnosis of prostate cancer

Prostate marker assays are widely used for detection of prostate cancer (PCa) but are associated with considerable sensitivity and specificity problems. Therefore, we investigated prostatic protein glycosylation profiles as a potential biomarker. We determined the urinary asparagine-linked glycan (N-glycan) profile of prostatic proteins of healthy volunteers (n = 25), patients with benign prostate hyperplasia (BPH; n = 62) and newly diagnosed PCa patients (n = 42) using DNA-sequencer-assisted fluorophore-assisted carbohydrate electrophoresis. Through squeezing of the prostate, a sufficient amount of prostatic proteins was obtained for direct structural analyses of N-glycan structures. N-glycans of PCa compared to BPH were characterized by a significant decrease in triantennary structures (p = 0.047) and overall fucosylation (p = 0.026). Prostate-specific antigen (PSA) and the urinary glycoprofile marker showed comparable overall receiver operating characteristic curve analysis as well as in the diagnostic gray zone with serum PSA values between 4 and 10 μg/L. However, when combining PSA and the urinary glycoprofile marker, the latter gave an additive diagnostic value to serum PSA (p ≤ 0.001). In conclusion, N-glycosylation profiling demonstrated differences between BPH and PCa. These changes could lead to the discovery of a new biomarker for PCa.

Glycosylation of prostate specific antigen and its potential diagnostic applications

Prostate specific antigen (PSA) assays are widely used for early detection of prostate cancer. However, those analyses are associated with considerable sensitivity and specificity problems. Several approaches have been developed to tackle this issue. PSA is a glycoprotein, which is primarily produced by the prostatic epithelial cells. Aberrant glycosylation modification of proteins is a fundamental characteristic of tumorigenesis. Study of PSA glycoforms offers interesting diagnostic perspectives. Modern technology allows us to analyze PSA glycoforms in a variety of clinical samples (serum or plasma, urine, seminal fluid, tissue). A number of novel techniques, such as lectin-based detection methods, mass spectrometry, 2-dimensional electrophoresis and capillary electrophoresis have been developed to analyze PSA glycosylation. This article reviews the technical and diagnostic aspects of PSA glycoforms.

A sensitive assay to measure biomarker glycosylation demonstrates increased fucosylation of prostate specific antigen (PSA) in patients with prostate cancer compared with benign prostatic hyperplasia

BACKGROUND

Prostate specific antigen (PSA) measurement is used for the diagnosis of prostate cancer (PCa) but the test lacks specificity due to the number of false positive readings. The glycosylation of PSA is altered in PCa but studies in this area have been limited to few clinical samples and/or require advanced laboratory facilities. An assay to assess PSA glycosylation was established using equipment available in most routine biomedical testing laboratories.

METHODS

Serum samples from patients with PCa or benign prostatic hyperplasia (BPH) were used. PSA (range 4-10 ng/ml) was affinity purified, separated and probed with the lectin Ulex europaeus (UEA-1; specific for α1,2 linked fucose). An enzyme-linked immunosorbent lectin assay (ELLA) with colorimetric detection was devised and PSA fucosylation assessed in a further independent set of 26 samples.

RESULTS

Free PSA (fPSA) from PCa patients showed a significant increase in fucosylation compared with fPSA from patients with BPH. The ELLA was 92% specific and 69% sensitive for PCa over BPH. In comparison, fPSA measurement was 70% specific and 56% sensitive (threshold set to 25% tPSA) for PCa over BPH.

CONCLUSIONS

Changes in glycosylation of PSA were identified using 50 μl of serum with PSA in the range of 4-10 ng/ml, this represents a more specific and sensitive test for PCa based on fucosylation changes of fPSA.

Predicting the outcome of prostate biopsy: comparison of a novel logistic regression-based model, the prostate cancer risk calculator, and prostate-specific antigen level alone

OBJECTIVES

To develop a logistic regression-based model to predict prostate cancer biopsy at, and compare its performance to the risk calculator developed by the Prostate Cancer Prevention Trial (PCPT), which was based on age, race, prostate-specific antigen (PSA) level, a digital rectal examination (DRE), family history, and history of a previous negative biopsy, and to PSA level alone.

PATIENTS AND METHODS

We retrospectively analysed the data of 1280 men who had a biopsy while enrolled in a prospective, multicentre clinical trial. Of these, 1108 had all relevant clinical and pathological data available, and no previous diagnosis of prostate cancer. Using the PCPT risk calculator, we calculated the risks of prostate cancer and of high-grade disease (Gleason score > or =7) for each man. Receiver operating characteristic (ROC) curves for the risk calculator, PSA level and the novel regression-based model were compared.

RESULTS

Prostate cancer was detected in 394 (35.6%) men, and 155 (14.0%) had Gleason > or =7 disease. For cancer prediction, the area under the ROC curve (AUC) for the risk calculator was 66.7%, statistically greater than the AUC for PSA level of 61.9% (P < 0.001). For predicting high-grade disease, the AUCs were 74.1% and 70.7% for the risk calculator and PSA level, respectively (P = 0.024). The AUCs increased to 71.2% (P < 0.001) and 78.7% (P = 0.001) for detection and high-grade disease, respectively, with our novel regression-based models.

CONCLUSIONS

ROC analyses show that the PCPT risk calculator modestly improves the performance of PSA level alone in predicting an individual's risk of prostate cancer or high-grade disease on biopsy. This predictive tool might be enhanced by including percentage free PSA and the number of biopsy cores.

A meta-analysis of the performance characteristics of the free prostate-specific antigen test

OBJECTIVES

To conduct a meta-analysis of the diagnostic performance of the percent free prostate-specific antigen (%fPSA) test in determining prostate cancer status and to assess its value in helping to decide whether to biopsy the prostate.

METHODS

Articles identified through a MEDLINE search were included if they presented adequate original primary data to calculate a receiver operating characteristic (ROC) curve in subjects possessing histopathologically verified diagnoses. Articles containing subjects with concurrent, non-prostate-related genitourinary conditions were excluded. Percent free PSA sensitivity, specificity, ROC curves, and positive likelihood ratios were calculated for all PSA ranges and for the reflex range of PSA between 4 and 10 ng/mL.

RESULTS

Among the 41 studies, containing 19,643 subjects, area under the curve for %fPSA was 0.70 for all PSA levels, decreasing to 0.68 in the reflex range. A test cutoff of 20% would lead to 92% sensitivity and 23% specificity. Positive likelihood ratios ranged from 1.0 to 4.0, exceeding 2.0 at %fPSA of 15% or less. Within the reflex range, however, likelihood ratios exceeded 2.0 only at %fPSA of 7% or less.

CONCLUSIONS

Percent free PSA can be a useful adjunct to PSA for primary prostate cancer screening only under certain defined situations. In the "gray zone," or reflex range, of PSA testing, %fPSA improves clinical information only when levels reach extreme values.

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.

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.

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.

Differences in prostate size between patients from University and Veterans Affairs Medical Center populations

BACKGROUND

Numerous studies on prostatic disease have been performed at Veterans Affairs (VA) Medical Centers. Recent investigations evaluating early detection of prostate cancer provide insight that the average prostate volume may be different between patients with similar clinical findings who are from different hospital settings. The objective of this study was to compare prostate size between men from University and VA Medical Centers.

METHODS

Patients were enrolled retrospectively from 1989-1996 from the Urology Clinics at a University and a VA Medical Center. All men underwent transrectal ultrasound-guided sextant biopsy of the prostate owing to either an elevated prostate-specific antigen (PSA) level and/or abnormal digital rectal examination (DRE) detected prior to biopsy. Prostate volume was calculated using the ellipsoid three-diameter formula based on transrectal ultrasound measurements.

RESULTS

There were 1,311 men included in the analysis: 717 were from the VA, and 594 were from the University. The average prostate volume was significantly smaller among VA patients both for men with cancer (P = 0.0004) and for men with no evidence of malignancy (P < 0.0001). Overall, the average prostate volume was 38.5 cm3 (median, 32.5 cm3) among men from the VA compared to 46.8 cm3 (median, 39.3 cm3) among men from the University Medical Center. Men from the VA were older (mean +/- SD = 68 +/- 7.3) than men from the University (mean +/- SD = 66 +/- 7.7) (P = 0.004) and there was no significant difference in PSA levels between the two groups of patients (P = 0.11). Intriguingly, the incidence of cancer was significantly lower at the VA (24.5%) compared to the University (35.9%) (P < 0.0001).

CONCLUSIONS

The variance in prostate size suggests that there are significant differences between the two patient populations. Proposed factors leading to this discrepancy include differences in socioeconomic factors, environmental factors, and changes in hormonal milieu related to alcohol and tobacco use. These results may have significant implications regarding the interpretation and extrapolation of results from previous studies performed at a single hospital setting.

Elevated serum prostate specific antigen levels in conjunction with an initial prostatic biopsy negative for carcinoma: who should undergo a repeat biopsy?

OBJECTIVE

To determine the outcome of repeated prostatic biopsies in men attending with suspected prostate cancer but an initial negative biopsy.

PATIENTS AND METHODS

Patients who had undergone two or more transrectal ultrasonography (TRUS)-guided prostate biopsies were identified from the Hospital Information Support System database. Indications for TRUS were a raised prostate-specific antigen (PSA) level (>4.0 ng/mL), with or without an abnormal digital rectal examination (DRE). Sextant prostate biopsies plus biopsies of any suspicious hypoechoic area or area of DRE abnormality were obtained for histology. Forty-eight patients underwent repeat TRUS-guided prostatic biopsies (mean age 67.5, sd 7. 25, range 53-82 years).

RESULTS

The mean (sd, median, range) PSA level was 16.9 (13.5, 11.6, 5.2-61.8) ng/mL. Fifteen patients (31%) had carcinoma on repeat biopsy, 11 after the second and four after a third biopsy. The positive repeat biopsy rate was 24% where the PSA level was 4.0-9.9 ng/mL, 33% if the level was 10.0-19.9 ng/mL and 39% if it was >/=20.0 ng/mL. There was no significant difference in age or initial PSA concentration between those men with positive and those with negative repeat biopsies. However, patients with cancer had significantly higher PSA levels before repeat biopsy than at first biopsy (P=0.0043) and had greater PSA velocities than had patients with no diagnosis of cancer (P=0.0067).

CONCLUSION

Where sufficient clinical suspicion exists, despite an initial negative biopsy, repeat TRUS-guided prostate biopsies should be carried out to exclude carcinoma of the prostate.

Measurement of complexed PSA improves specificity for early detection of prostate cancer

OBJECTIVES

Prostate-specific antigen (PSA) is the most useful of all tumor markers. Although the sensitivity is impressive, low specificity results in a lack of cancer detection in a significant proportion of patients undergoing prostate biopsy. Several recent studies have addressed the need for improved specificity. Of all these approaches, the free/total PSA ratio appears to be the most promising. Given that most circulating PSA is complexed to alpha1-antichymotrypsin, and that this moiety represents a greater proportion of the total PSA in those men with carcinoma, we set out to determine whether complexed PSA would improve specificity in the detection of men with prostate cancer.

METHODS

Archival sera were obtained from 300 men, 75 of whom had biopsy-proved prostate cancer. All sera had been previously stored at -70 degrees C for variable periods. An investigative assay for complexed PSA (Bayer) was used. The Tandem-R free and total PSA assays (Hybritech) were used according to the manufacturer's recommendations.

RESULTS

Among all patients, specificities for the total PSA, free/total PSA, and complexed PSA alone were 21.8%, 15.6%, and 26.7%, respectively, at cutoffs yielding 95% sensitivity. Similar equivalence or superior performance, in terms of specificity relative to the free/total PSA ratio, was seen at other sensitivity thresholds and other total PSA ranges.

CONCLUSIONS

Complexed PSA alone performs better than total PSA or the free/total PSA ratio and obviates the need for a second analyte determination. We believe this marker may offer significant enhancement in PSA testing with significant economic advantages.

Prostate-specific antigen and new related markers for prostate cancer

Although prostate-specific antigen (PSA), or human kallikrein 3, is the most valuable tool available for the diagnosis and management of prostate cancer, as currently used it is insufficiently sensitive and specific for early detection or staging of the malignancy. Many new concepts have been introduced in order to optimize the clinical use of PSA measurements, but each one has its own drawbacks. The molecular forms of PSA, especially the free PSA, seem to be useful for the detection of prostate cancer in men with PSA concentrations falling in the 4-10 microg/l range. New molecular techniques, such as reverse transcriptase polymerase chain reaction for the detection of minimal amounts of PSA messenger RNA and prostate-specific membrane antigen, offer new promise for the prognosis and possibly staging of prostate cancer. On the other hand, human kallikrein 2, a serine protease closely related to PSA that is also expressed predominantly in the prostate, may be a new adjuvant marker for prostate cancer. As for its biological functions, PSA can no longer be regarded as a specific prostate molecule associated mainly with semen liquefaction when it has a possible role as a prognostic indicator in female breast cancer. The biological role of PSA in normal tissues and tumors may be much more complex than previously thought and requires further investigation.

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.

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.

Free-to-total prostate-specific antigen (PSA) ratio improves the specificity for detecting prostate cancer in patients with prostatism and intermediate PSA levels

OBJECTIVE

To investigate the clinical significance of the free-to-total prostate-specific antigen (PSA) ratio in improving the specificity of PSA measurement for detecting prostate cancer within the diagnostic intermediate range (4-10 ng/mL total PSA) in patients referred for the treatment of urinary symptoms.

PATIENTS AND METHODS

Serum samples were obtained from 333 consecutive patients with obstructive and irritative urinary symptoms. Of these men, 114 had total PSA levels of 4-10 ng/mL; 22 had prostate cancer (group 1) and 71 had benign prostatic hyperplasia (BPH, group 2). Group 3 consisted of 21 patients with BPH and a chronic indwelling catheter. The concentrations of free and total PSA (ProStatus, Wallac Oy, Turku, Finland) and PSA complexed to alpha-1-antichymotrypsin were measured and the free-to-total PSA ratio calculated. All patients under 70 years of age or with suspicious findings on digital rectal examination or transrectal ultrasonography underwent ultrasound-guided sextant prostate biopsies. Of the 114 patients, 105 (92%) underwent transurethral resection of the prostate and six (5%) radical retropubic prostatectomy.

RESULTS

Patients in group 1 had significantly lower median free PSA concentrations (0.78 ng/mL vs 1.13 ng/mL, P < 0.001) and a lower free-to-total PSA ratio (12.1% vs 19.9%, P < 0.001) than those in group 2. The differences were similar between group 1 and group 3 (median free PSA in group 3, 1.06 ng/mL, P = 0.03, and free-to-total PSA ratio 18.7%, P = 0.007). There were no significant differences between patients in groups 2 and 3. The free-to-total PSA ratio had a higher specificity than total PSA at all sensitivity levels, e.g. a threshold free-to-total PSA ratio of 0.20 detected 91% of cancers and spared 48% (group 2) or 46% (group 3) from unnecessary biopsies. The area under the receiver operating characteristic curve for group 1 vs group 2 was 0.56 (total PSA) and 0.78 (free-to-total PSA ratio) and for group 1 vs group 3 was 0.56 (total PSA) and 0.81 (free-to-total PSA ratio).

CONCLUSION

In those patients with extensive symptoms from BPH and requiring surgical treatment, the free-to-total PSA ratio improves the specificity for detecting prostate cancer in the diagnostic 'grey zone' of 4-10 ng/mL total PSA. This improvement occurred in patients with or without a chronic indwelling catheter for urinary retention.