Comparisons of the various combinations of free, complexed, and total prostate-specific antigen for the detection of prostate cancer

Development of simultaneous detection of total prostate-specific antigen (tPSA) and free PSA with rapid bead-based immunoassay

OBJECTIVE

Prostate-specific antigen (PSA) is the most important biochemical tumor marker for the early detection of prostate cancer; however, its diagnostic specificity is low. Therefore, free PSA (fPSA) test is recommended as an adjunct to increase the specificity. However, all the current technology only allows detecting one biomarker at one time. In this study, we reported a flexible bead-based immunoassay to measure total PSA (tPSA) and fPSA simultaneously.

MATERIALS AND METHODS

We used the Luminex xMAP bead array technology to measure tPSA and fPSA at one time, employing two mouse monoclonal anti-PSA antibodies (5G6 and 8A6) for coating and another mouse monoclonal anti-PSA antibody (5A6) for detection. Then we compared the data of Luminex assay with that of the conventional enzyme-linked immunosorbent assay (ELISA).

RESULTS

The assay was fast with a wide dynamic range. The lower detection limit for tPSA and fPSA were 2.3 and 1.3  pg/ml. The inter-assay coefficients for tPSA and fPSA were between 5.64 and 7.65%, and the intra-assay coefficients for tPSA and fPSA were between 4.15 and 5.89%. A close correlation between the new assay and the conventional ELISA was observed.

CONCLUSIONS

The bead-based platform is rapid, sensitive, and less expensive, which allows both single sample and high-throughput measurement of tPSA and fPSA over a wide range of concentrations.

Peripheral zone prostate cancer in patients with elevated PSA levels and low free-to-total PSA ratio: detection with MR imaging and MR spectroscopy

PURPOSE

To retrospectively assess the value of endorectal magnetic resonance (MR) imaging and MR spectroscopy combined with the free-to-total prostate-specific antigen (PSA) ratio for detecting prostate cancer in men with elevated PSA levels.

MATERIALS AND METHODS

The institutional review board approved the study, and all patients provided informed written consent. Endorectal MR imaging and MR spectroscopy were performed in 54 patients with PSA levels greater than 3 ng/mL but less than 15 ng/mL and free-to-total PSA ratio of less than 20%, followed by sextant biopsy in the peripheral zone. For each patient, MR imaging and MR spectroscopic findings, PSA level, and free-to-total PSA ratio were analyzed and compared with biopsy results and/or histopathologic tumor maps with regard to a sextant-modified distribution. The likelihood of cancer in each sextant according to MR and MR spectroscopic findings was graded independently on a scale of 1 (benign) to 5 (malignant). Detection accuracy and a multivariate logistic regression analysis were used to determine the most accurate combination of imaging, and clinical tests were used to detect prostate cancer according to the area under the receiver operating characteristic curve (AUC).

RESULTS

The model incorporating MR imaging, MR spectroscopy, and free-to-total PSA ratio (AUC = 97.5%) was significantly more accurate in predicting prostate cancer than models using MR imaging alone (AUC = 85.1%; P = .007), MR spectroscopy alone (AUC = 87.2%; P = .041), or MR imaging and free-to-total PSA ratio combined (AUC = 90.8%; P = .038).

CONCLUSION

MR and MR spectroscopy combined with free-to-total PSA ratio improves the predictive value for prostate cancer detection.

Derivatives of prostate-specific antigen as predictors of incidental prostate cancer

OBJECTIVE To search for an optimal derivative of prostate-specific antigen (PSA) identifying patients at risk of incidental prostate cancer. PATIENTS AND METHODS In all, 693 patients who underwent transurethral resection of the prostate (TURP) with a normal digital rectal examination, no history of prostate cancer and a PSA level of 2.5-10 ng/mL were studied. The total PSA (tPSA), percentage of free/total PSA (%fPSA), complexed PSA (cPSA), PSA density, cPSA density and the ratio of fPSA to cPSA were measured. Specificity, sensitivity, positive and negative predictive values were determined for all possible threshold values indicating the risk of incidental prostate cancer (T1a or T1b). Furthermore, the patients were subdivided according to age and the presence of an indwelling transurethral catheter. The areas under the receiver operating characteristic curves (AUC) were compared. RESULTS In the whole sample, the %fPSA was the best test predicting all incidental prostate cancers (AUC 0.618, reference: tPSA 0.494), whereas cPSA density was the best predictor of T1b disease (AUC 0.720, reference: tPSA 0.548). Stratification by age did not meaningfully alter the results, the presence of a transurethral catheter, however, was associated with a superiority of tests based on fPSA (AUC 0.620-0.670) compared with tests based on tPSA or cPSA (AUC 0.421-0.581). CONCLUSION Replacing tPSA by PSA derivatives (%fPSA or cPSA density) and stratifying by the presence of an indwelling transurethral catheter may improve the prediction of the risk of incidental prostate cancer and spare unnecessary biopsies before TURP in the tPSA range 2.5-10 ng/mL.

[PSA and hK2 in the diagnosis of prostate cancer]

Serum markers for prostate carcinoma are widely applied for the purpose of early detection of cancer and the differentiation between benign and malignant disease, for the pre-treatment staging of detected prostatic cancers, and for the monitoring of prostate cancer after curative or palliative therapies. Since its discovery in 1979, serum PSA has been the most powerful marker of prostate cancer, but, when used alone, PSA is not sufficiently sensitive or specific to consider it an ideal tool for the early detection or staging of prostate cancer. To optimize the use of PSA, the concepts of PSA velocity, PSA density, and age-related PSA values were developed. Moreover, the molecular forms of PSA, especially the percentage of free PSA, seem to be useful tools for the detection of prostate cancer in men with slightly elevated total PSA. Human kallikrein 2 (hK2), a serine protease closely related to PSA that also is expressed predominantly in the prostate, is a new complementary marker to PSA for early detection of prostate cancer. In this review, we examine PSA testing and its effectiveness in the diagnosis of prostate cancer. Further, we also evaluate recent literature regarding the use of hk2.

Evaluating the validity of blood-based membrane potential changes for the identification of bipolar disorder I

OBJECTIVE

The objective of this study was to develop a diagnostic blood test for bipolar disorder I using membrane potentials as biological markers.

METHODS

We measured the fluorescence intensity of a dye sensitive to membrane potential in whole blood samples from bipolar I, unipolar, schizophrenic patients, and psychiatrically normal controls. Patients were diagnosed through structured clinical interviews according to DSM-IV. Both the t-test and logistic regression analysis were used to analyze the data.

RESULTS

The membrane potential as indicated by the fluorescence intensity of the membrane potential dye in blood cells drawn from patients with bipolar disorder I was significantly different from the blood cells drawn from unipolar and schizophrenic patients, and from psychiatrically normal controls (P<0.001). The specificity and sensitivity were determined to be 0.88 and 0.78 respectively which compared well with the state of the art diagnostic techniques for other diseases. Logistic regression analysis revealed that the membrane potential was a reliable predictor which could be used as a diagnostic marker for bipolar I.

CONCLUSIONS

These results indicate that the membrane potential of blood cells can be used as a diagnostic marker to augment the DSM-IV diagnosis of bipolar disorder I. Expanded clinical trials are needed to establish this technique for general use.

Use of prostate-specific antigen (PSA) isoforms for the detection of prostate cancer in men with a PSA level of 2-10 ng/ml: systematic review and meta-analysis

OBJECTIVE

Measurement of serum prostate-specific antigen (PSA) for the detection of prostate cancer has poor specificity in men with PSA levels between 2 and 10 ng/ml. It has been suggested that measurement of the ratio of free to total PSA (f/tPSA) or complexed PSA (cPSA) might offer an improvement. We performed a systematic review and meta-analysis to evaluate the diagnostic performance of these tests among men with PSA levels between 2 and 10 ng/ml.

METHODS

Data on sensitivity and specificity were extracted from 66 eligible studies. Likelihood ratios and summary receiver operating characteristic curves were estimated and possible sources of heterogeneity between studies examined.

RESULTS

Use of the f/tPSA or the cPSA test improved diagnostic performance among men with a total PSA (tPSA) of 2-4 or 4-10 ng/ml compared to tPSA alone. The diagnostic performance of the f/tPSA test was significantly higher in the tPSA range of 4-10 ng/ml compared to a tPSA range of 2-4 ng/ml (p < 0.01); at a sensitivity of 95%, the specificity was 18% in the 4-10 ng/ml tPSA range and 6% in the 2-4 ng/ml tPSA range. Among studies that measured both isoforms, the diagnostic performance of the f/tPSA test and the cPSA was equivalent in both PSA ranges.

CONCLUSIONS

The use of the f/tPSA or cPSA test among men with PSA levels between 2 and 10 ng/ml can reduce the number of unnecessary biopsies whilst maintaining a high cancer detection rate.

Role of tissue polypeptide specific antigen in the detection of prostate cancer

OBJECTIVE

The aim of the present study was to evaluate the role of tissue polypeptide specific antigen (TPS) in the diagnosis of different stages of prostatic cancer (CaP) and to compare the diagnostic efficacy of serum TPS in respect to total prostate-specific antigen (tPSA) and free/total (f/t) PSA ratio.

PATIENTS AND METHODS

Patients with BPH (n = 58), localized CaP (n = 37) and metastatic CaP (n = 16) were compared by measuring serum TPS, tPSA and f/t PSA ratio.

RESULTS

Serum TPS was significantly increased only in patients with metastatic CaP (p < 0.05) and TPS levels was not significantly different between patients with BPH and localized CaP. Both f/tPSA and tPSA showed better sensitivity, specificity and receiver operating curve analysis in the differential diagnosis of BPH and localized CaP.

CONCLUSION

In conclusion, serum TPS measurement was found to be significantly increased in metastatic prostatic carcinoma cases but was not useful in the early detection of prostatic carcinoma. Although there are several studies demonstrating the usefulness of TPS in the differential diagnosis of prostate cancer, there is increasing evidence for the use of this molecule in the late period of the disease or as an adjunct to other molecules in the detection of recurrences.

Predictors of prostate cancer on repeat prostatic biopsy in men with serum total prostate-specific antigen between 4.1 and 10 ng/mL

OBJECTIVES

We determine whether the different molecular forms of prostate-specific antigen (PSA) and other PSA variables can predict prostate cancer in men undergoing repeat prostate needle biopsy.

METHODS

Between 1997 and 2001, repeat biopsy was performed in 97 patients who had undergone prior negative prostate biopsy. The ability of total PSA (tPSA), complexed PSA (cPSA), free PSA (fPSA), free-to-total PSA (fPSA/tPSA), free-to-complexed PSA (fPSA/cPSA), complexed-to-total PSA (cPSA/tPSA), tPSA density (tPSAD), cPSA density (cPSAD), transition zone tPSA density (tPSATZ) and transition zone cPSA density (cPSATZ) was assessed by univariate and multivariate analyzes as well as receiver operating characteristics (ROC) curves.

RESULTS

Prostate cancer on repeat biopsy was detected in 24% of subjects (23 of 97) who had a negative initial biopsy. The PSA parameters cut-off to ensure a 96% sensitivity of cancer detection, were 29% using fPSA/tPSA, 32% using fPSA/cPSA, 0.18 ng/mL/cc using tPSATZ and 0.16 ng/mL/cc using cPSATZ. The fPSA/tPSA would have prevented 32% of negative biopsies, the fPSA/cPSA 28%, the tPSATZ 23% and the cPSATZ 30%. ROC curve analysis fPSA/tPSA, fPSA/cPSA ratios, tPSATZ and cPSATZ were significantly better predictors of repeat biopsy results than tPSA or cPSA, but there was no significant difference in the ROC curves among these four PSA parameters. In the multivariate logistic regression analysis these four PSA parameters were significant predictors for cancer detection in the repeat biopsy group (P < 0.001).

CONCLUSION

fPSA/tPSA ratio, fPSA/cPSA ratio, tPSATZ and cPSATZ enhance the specificity of PSA testing compared to tPSA or cPSA when determining which patients should undergo repeat biopsy.

Evaluation of the clinical performance of equimolar- and skewed-response total prostate-specific antigen assays versus complexed and free PSA assays and their ratios in discriminating between benign prostatic hyperplasia and prostate cancer

BACKGROUND

Prostate-specific antigen (PSA) exists in human serum in two principal forms, free PSA (fPSA) and protein-complexed PSA, predominantly PSA-ACT (alpha(1)-antichymotrypsin). Equimolar response (EMR) total PSA (tPSA) immunoassays measure each of these forms equally while skewed-response (SKR) assays overestimate or underestimate the tPSA concentration. The advantages of EMR over SKR tPSA assays are controversial.

METHODS

We used five nonhuman serum-based samples each containing a different proportion of fSPA:PSA-ACT (0:100 to 100:0, %:%) and patients' serum samples from men with histologically confirmed benign prostatic hyperplasia (BPH) (n=94) or PCA (n=30) and a wide range of fPSA concentrations to investigate the molar response status of six tPSA assays. Receiver-operator characteristic (ROC) curve analysis was used to compare the discriminatory power of these assays in distinguishing men with BPH from those with PCA.

RESULTS

The Bayer Immuno-1 tPSA (BtPSA) assay demonstrated EMR characteristics and diagnostic accuracy similar to the Hybritech Tandem-E and Tandem-R tPSA assays. At 90% sensitivity, EMR tPSA assays had higher specificity than SKR tPSA assays.

CONCLUSIONS

The BtPSA assay is an EMR tPSA assay and EMR assays provide improved diagnostic specificity over SKR tPSA assays.

Complexed prostate-specific antigen for early detection of prostate cancer in men with serum prostate-specific antigen levels of 2 to 4 nanograms per milliliter

Complexed PSA (cPSA) has been shown to improve specificity in the detection of prostate cancer over that of total PSA (tPSA) testing in men with tPSA values greater than the cutoff value of 4.0 ng/mL. However, recent studies have reported a 25% incidence of prostate cancer in men with tPSA values in the 2.5- to 4.0-ng/mL range. We performed a multicenter study of cPSA in a population of men who underwent prostate biopsies because of elevated PSA levels or abnormal digital rectal examination (DRE). As part of this study, we sought to assess the clinical value of cPSA in comparison to tPSA, the free/tPSA ratio (f/tPSA) and the complexed/tPSA ratio (c/tPSA) in early detection of prostate cancer in men with tPSA values in the range of 2 to 4 ng/mL. The study was performed at 7 centers. Sera were drawn from men who underwent biopsy procedures consisting of >10 prostate tissue cores. Receiver operating characteristic (ROC) analysis was performed from the results of patients with tPSA values in the range of 2 to 4 ng/mL, including men with suspicious as well as unremarkable findings on DRE. Sera were collected and tested with the Bayer tPSA and cPSA assay and the Beckman free PSA and tPSA assays. ROC analysis was performed for all samples in the 2- to 4-ng/mL PSA range. At biopsy, 158 men had no evidence of malignancy and 57 (26.5%) were diagnosed with prostate cancer. ROC analysis indicated that the area under the curve (AUC) for cPSA was 0.64, which was statistically significantly greater than that achieved for tPSA (AUC, 0.57; P <0.0001). The AUC for f/tPSA and c/tPSA were 0.60 and 0.63, respectively, which was not statistically significantly different from that of tPSA or cPSA (P >or=0.252). A cutpoint of 2.5 ng/mL for tPSA and 2.1 ng/mL for cPSA provided a specificity of 20.3% and 34.2%, respectively, and sensitivity levels of 86%. Using cutpoints of 25% for f/tPSA and 74% for c/tPSA provided a specificity of 11.0% and 21.5%, respectively, and sensitivity levels of 97%. In all, >92% of the cancers treated with radical prostatectomy were organ confined, and the histologic grading of the tumors ranged from moderately to poorly differentiated with Gleason scores from 5 to 9. These data confirm that there is a high incidence of clinically significant prostate cancer in men with tPSA levels <4.0 ng/mL. Measurement of cPSA proved useful in stratifying men with tPSA values in the 2- to 4-ng/mL range into high- and low-risk groups for prostate cancer. The use of cPSA as a single test was found to enhance detection of prostate cancer over that of testing with tPSA and PSA ratios in men with tPSA values in the range of 2 to 4 ng/mL.

Prognostic value of three molecular forms of prostate-specific antigen ratios in patients with prostate adenocarcinoma

OBJECTIVES

To investigate whether different molecular forms of prostate-specific antigen (PSA) ratios could provide prognostic information about the stage and grade of prostate cancer.

METHODS

Serum specimens were examined from 53 patients who underwent radical prostatectomy for clinically localized prostate cancer and from 94 patients diagnosed as having no evidence of malignancy (total PSA between 4.1 and 20.0 ng/mL). The free/total PSA (fPSA/tPSA) ratio and complexed/total PSA (cPSA/tPSA) ratio in 18 patients with biochemical recurrence were compared with those of patients either without recurrence or with no evidence of malignancy.

RESULTS

The fPSA/tPSA and cPSA/tPSA ratios differed significantly (P <0.05) between patients with organ-confined and those with non-organ-confined disease, but the tPSA, cPSA, and fPSA levels did not (P >0.05). The median values of the fPSA/tPSA ratio in patients with recurrence (7.0%) were significantly lower than in the patients without recurrence (8.9%) or those without evidence of malignancy (15.2%) (P = 0.02 and P <0.01, respectively). The median values of the cPSA/tPSA ratio in patients with recurrence (97.4%) were significantly higher than in patients without recurrence (92.9%) or those without evidence of malignancy (86.7%) (P <0.01 and P <0.01, respectively). At the time of recurrence, 6 (33%) of 18 patients expressed higher fPSA/tPSA ratios (15% or greater) and lower cPSA/tPSA ratios (less than 95%). Five (83%) of these 6 patients appeared to have aggressive tumors according to pathologic stage.

CONCLUSIONS

The fPSA/tPSA and cPSA/tPSA ratios differed significantly among the three groups. Thus, a subset of tumors appears to be capable of producing high fPSA/tPSA and low cPSA/tPSA ratios at the time of recurrence, and some of these have an aggressive phenotype. Until this latter phenomenon can be adequately explained, use of these ratios for prognostic purposes should be approached cautiously.