Although case-control studies have identified numerous single nucleotide polymorphisms (SNPs) associated with prostate cancer, the clinical role of these SNPs remains unclear.
Evaluate previously identified SNPs for association with prostate cancer and accuracy in predicting prostate cancer in a large prospective population-based cohort of unscreened men.
Design, setting, and participants
This study used a nested case-control design based on the Malmö Diet and Cancer cohort with 943 men diagnosed with prostate cancer and 2829 matched controls. Blood samples were collected between 1991 and 1996, and follow-up lasted through 2005.
We genotyped 50 SNPs, analyzed prostate-specific antigen (PSA) in blood from baseline, and tested for association with prostate cancer using the Cochran-Mantel-Haenszel test. We further developed a predictive model using SNPs nominally significant in univariate analysis and determined its accuracy to predict prostate cancer.
Results and limitations
Eighteen SNPs at 10 independent loci were associated with prostate cancer. Four independent SNPs at four independent loci remained significant after multiple test correction (p < 0.001). Seven SNPs at five independent loci were associated with advanced prostate cancer defined as clinical stage ≥T3 or evidence of metastasis at diagnosis. Four independent SNPs were associated with advanced or aggressive cancer defined as stage ≥T3, metastasis, Gleason score ≥8, or World Health Organization grade 3 at diagnosis. Prostate cancer risk prediction with SNPs alone was less accurate than with PSA at baseline (area under the curve of 0.57 vs 0.79), with no benefit from combining SNPs with PSA. This study is limited by our reliance on clinical diagnosis of prostate cancer; there are likely undiagnosed cases among our control group.
Only a few previously reported SNPs were associated with prostate cancer risk in the large prospective Diet and Cancer cohort in Malmö, Sweden. SNPs were less useful in predicting prostate cancer risk than PSA at baseline.
Prostate cancer; Biomarkers; SNPs; PSA; Sensitivity and specificity
Prostate specific antigen (PSA) is a widely used and clinically valuable marker for prostate disease. In order to enable the development of new PSA assays and progress the understanding of the biology of PSA we have analyzed PSA in seminal plasma.
Design and Methods
PSA in seminal plasma from men attending a fertility clinic and healthy controls was analyzed using SDS-PAGE, Western blotting and mass spectrometry.
Using mass spectrometry, different forms of PSA could be identified in 1–9 bands seen on SDS-PAGE analysis of the respective sample. However, a majority of these molecular forms of PSA were not observed on Western blots. Enzymatic activity of PSA isoforms was demonstrated by sequencing data in zymogram gels. Multivariate analysis of clinical data revealed well-separated patient groups.
We demonstrated that PSA in seminal plasma occurs in several isoforms, yet not all were detectable using an antibody based clinical routine method. The heterogeneity of PSA expression might be of clinical significance, by an improved patient phenotyping.
prostate specific antigen; isoform; seminal plasma; infertility; MALDI LTQ Orbitrap XL; ESI-LTQ FT-ICR
To assess variation of total prostate-specific antigen (tPSA), free PSA (fPSA), percent fPSA, human glandular kallikrein 2 (hK2), and intact PSA measured three times within two weeks. Knowledge of the variation in an individual’s PSA level is important for clinical decision-making.
Patients and Methods
Study participants were 149 patients referred for prostate biopsy, of which 97 had benign disease and 52 had prostate cancer. Three blood samples were drawn with a median of four hours between first and second samples and 12 days between first and third samples. Variability was described by absolute differences, ratios and intra-individual coefficients of variation. Total PSA, fPSA, hK2, and intact PSA were measured in anti-coagulated blood plasma.
At baseline, the median tPSA was 6.8 (IQR 4.5, 9.6) ng/mL. The intra-individual variation was low for all biomarkers, and lowest for tPSA. For 80% of participants, the ratio between first and second time points for tPSA was between 0.91 and 1.09 and the ratio for percent fPSA was between 0.89 and 1.15. Total coefficients of variation between time 1 and 2 for tPSA, fPSA, percent fPSA, hK2 and intact PSA were 4.0%, 6.6%, 6.0%, 9.2%, and 9.5%, respectively. The measurements taken several days apart varied more than those taken on the same day, but the variation between both time points were not large.
The intra-individual variation for all the kallikrein-like markers studied was relatively small, especially for samples drawn the same day. Few cases are reclassified between the time points. This indicates high short-term biological and technical reproducibility of the tests in clinical use.
Free PSA; Prostate cancer; PSA; Screening; Variation
The introduction of total prostate specific antigen (total PSA) testing in blood has revolutionized the detection and management of men with prostate cancer (PCa). The objective of this review was to discuss the challenges of PCa biomarker research, definition of the type of PCa biomarkers, the statistical considerations for biomarker discovery and validation, and to review the literature regarding total PSA velocity and novel blood-based biomarkers.
An English-language literature review of the Medline database (1990 to August 2010) of published data on blood-based biomarkers and PCa was undertaken.
The inherent biological variability of total PSA levels affects the interpretation of any single result. Men who will eventually develop PCa have increased total PSA levels years or decades before the cancer is diagnosed. Total PSA velocity improves predictiveness of total PSA only marginally, limiting its value for PCa screening and prognostication. The combination of PSA molecular forms and other biomarkers improve PCa detection substantially. Several novel blood-based biomarkers such as human glandular kallikrein 2 (hK2), urokinase plasminogen activator (uPA) and its receptor (uPAR), transforming growth factor-beta 1 (TGF-β1); interleukin-6 (IL-6) and its receptor (IL-6R) may help PCa diagnosis, staging, prognostication, and monitoring. Panels of biomarkers that capture the biologic potential of PCa are in the process of being validated for PCa prognostication.
PSA is a strong prognostic marker for long-term risk of clinically relevant cancer. However, there is a need for novel biomarkers that aid clinical decision making about biopsy and initial treatment. There is no doubt that progress will continue based on the integrated collaboration of researchers, clinicians and biomedical firms.
Prostate neoplasms; molecular markers; prostate specific antigen
Percentage of free-to-total prostate-specific antigen (%fPSA) is an independent predictor of risk for prostate cancer among men with modestly elevated level of total PSA (tPSA) in blood. Physiological and pathological factors have been shown to influence the %fPSA value and diagnostic accuracy.
To evaluate genetic determinants of %fPSA, we conducted a genome-wide association study of serum %fPSA by genotyping 642,584 single nucleotide polymorphisms (SNPs) in 3192 men of European ancestry, each with a tPSA level of 2.5 to 10 ng/ml, that were recruited in the REduction by DUtasteride of Prostate Cancer Events study. Single nucleotide polymorphisms (SNPs) with P < 10-5 were further evaluated among the controls of a population-based case-control study in Sweden (2899 prostate cancer cases and 1722 male controls), including 464 controls having tPSA levels of 2.5 to 10 ng/ml.
We identified two loci that were associated with %fPSA at a genome-wide significance level (P <5 x 10-8). The first associated SNP was rs3213764 (P = 6.45 x 10-10), a nonsynonymous variant (K530R) in the ATF7IP gene at 12p13. This variant was also nominally associated with tPSA (P = .015). The second locus was rs1354774 (P = 1.25 x 10-12), near KLK2 at 19q13, which was not associated with tPSA levels, and is separate from the rs17632542 locus at KLK3 that was previously associated with tPSA levels and prostate cancer risk. Neither rs3213764 nor rs1354774 was associated with prostate cancer risk or aggressiveness.
These findings demonstrate that genetic variants at ATF7IP and KLK2 contribute to the variance of %fPSA.
Prostate specific antigen (PSA), as a widely used clinical biomarker in prostate cancer diagnostics, exists in multiple molecular forms. However, all of these forms might not be recognized in a given sample by the standard immunoassays. Therefore, we have investigated PSA isoforms separated by size using mass spectrometric analyses. The objective of these developments was to identify and specify the various forms of PSA. To optimize successful identification of different PSA forms, we have developed a bioinformatic strategy, consisting of high resolution MALDI-MS PMF and sequencing MS/MS data searches. To improve sequence-based identification, the recently introduced Proteios software environment was employed, allowing the combination of multiple database search engines in an automated manner.
We could unambiguously identify PSA in clinical samples by all detectable tryptic peptides, which were found to be common in several isoforms.
prostate specific antigen isoforms; MALDI LTQ Orbitrap XL; ESI-LTQ FT-ICR; Proteios software environment; kallikrein-2
Abiraterone acetate (AA) is an androgen biosynthesis inhibitor shown to prolong life in patients with castration-resistant prostate cancer (CRPC) already treated with chemotherapy. AA treatment results in dramatic declines in prostate-specific antigen (PSA) in some patients and no declines in others, suggesting the presence of molecular determinants of sensitivity in tumors.
To study the role of transmembrane protease, serine 2 (TMPRSS2)–v-ets erythroblastosis virus E26 oncogene homolog (ERG) fusion, an androgen-dependent growth factor, in circulating tumor cells (CTCs) as a biomarker of sensitivity to AA.
Design, setting, and participants
The predictive value of TMPRSS2-ERG status was studied in 41 of 48 men with postchemotherapy-treated CRPC enrolled in sequential phase 2 AA trials.
Patients received AA 1000 mg daily and continuously.
TMPRSS2-ERG status was characterized by a sensitive, analytically valid reverse transcription polymerase chain reaction assay in CTCs enriched from ethylene-diaminetetraacetic acid anticoagulated blood obtained prior to AA treatment. Outcomes were measured by PSA Working Group 1 criteria.
Results and limitations
Standard procedures for specimen acquisition, processing, and testing using the validated TMPRSS2-ERG assay on a multiplex platform gave intra-assay and interassay coefficients of variation <7%. TMPRSS2-ERG fusion was present in 15 of 41 patients (37%), who had a median baseline CTC count of 17 (interquartile range: 7–103 cells per 7.5 ml). A PSA decline ≥50% was observed in 7 of 15 patients (47%) with the fusion and in 10 of 26 patients (38%) without the fusion. Although limited by the low number of patients, a posttherapy CTC count of less than five per 7.5 ml was prognostic for longer survival relative to a CTC count five or more. TMPRSS2-ERG status did not predict a decline in PSA or other clinical outcomes.
Molecular profiles of CTCs with an analytically valid assay identified the presence of the prostate cancer–specific TMPRSS2-ERG fusion but did not predict for response to AA treatment. This finding demonstrates the role of CTCs as surrogate tissue that can be obtained in a routine practice setting.
Abiraterone; Biomarker; Circulating tumor cells; Prostate cancer; Prostate-specific antigen; TMPRSS2-ERG fusion
A sophisticated reading of the randomized trial evidence suggests that, although screening for prostate cancer with prostate-specific antigen (PSA) can reduce cancer-specific mortality, it does so at considerable cost in terms of the number of men who need to be screened, biopsied, and treated to prevent one death. The challenge is to design screening programs that maximize benefits (reducing prostate cancer mortality) and minimize costs (overtreatment). Recent research has suggested that this can be achieved by risk-stratifying screening and biopsy; increasing reliance on active surveillance for low-risk cancer; restricting radical prostatectomy to high-volume surgeons; and using appropriately high-dose radiotherapy. In current U.S. practice, however, many men who are screened are unlikely to benefit, most men found to have low-risk cancers are referred for unnecessary curative treatment, and much treatment is given at low-volume centers.
prostatic neoplasms; prostate-specific antigen (PSA); surgery; radiotherapy
Prostate specific antigen (PSA) velocity has been proposed as a marker to aid detection of prostate cancer. We sought to determine whether PSA velocity could predict the results of repeat biopsy in men with persistently elevated PSA after initial negative biopsy.
Materials and Methods
We identified 1,837 men who participated in the Göteborg or Rotterdam section of the European Randomized Screening study of Prostate Cancer (ERSPC), and who had one or more subsequent prostate biopsies after an initial negative finding. We evaluated whether PSA velocity improved predictive accuracy beyond that of PSA alone.
There were a total of 2579 repeat biopsies, of which 363 (14%) were positive for prostate cancer, and 44 (1.7%) were high grade (Gleason score ≥7). Although PSA velocity was statistically associated with cancer risk (p<0.001), it had very low predictive accuracy (area-under-the-curve [AUC] of 0.55). There was some evidence that PSA velocity improved AUC compared to PSA for high grade cancer. However, the small increase in risk associated with high PSA velocity – from 1.7 % to 2.8% as velocity increased from 0 to 1 ng / ml / year - is of questionable clinical relevance.
Men with a prior negative biopsy have a lower risk for prostate cancer at subsequent biopsies, with high grade disease particularly rare. We found little evidence to support the use of PSA velocity to aid decisions about repeat biopsy for prostate cancer.
We previously reported that a single prostate-specific antigen (PSA) measured at age 44–50 was highly predictive of subsequent prostate cancer diagnosis in an unscreened population. Here we report an additional seven years of follow-up. This provides a replication on an independent data set, and allows estimates of the association between early PSA and subsequent advanced cancer (clinical stage ≥T3 or metastases at diagnosis).
Blood was collected from 21,277 men in a Swedish city (74% participation rate) during 1974–1986 at age 33–50. Through 2006, prostate cancer was diagnosed in 1408 participants; we measured PSA in archived plasma for 1312 (93%) of these cases and for 3728 controls.
At a median follow-up of 23 years, baseline PSA was strongly associated with subsequent prostate cancer (area-under-the-curve 0.72; 95% CI 0.70, 0.74; for advanced cancer 0.75; 95% CI 0.72, 0.78). Associations between PSA and prostate cancer were virtually identical for the initial and replication data sets with 81% (95% CI 77%, 86%) of advanced cases found in men with PSA above the median (0.63 ng/ml at age 44 – 50).
A single PSA at or before age 50 predicts advanced prostate cancer diagnosed up to 30 years later. Use of early PSA to stratify risk would allow a large group of men to be screened less often but increase frequency of testing on a more limited number of high-risk men. This is likely to improve the ratio of benefits to harms for screening.
prostate cancer; prostate-specific antigen; human kallikrein 2; risk factors; case-control study
Evidence of reduced prostate cancer mortality from randomized trials in Europe supports early detection of prostate cancer with prostate-specific antigen (PSA). Yet PSA screening has generated considerable controversy: it is far from clear that the benefits outweigh risks, in terms of overdiagnosis and overtreatment. One way to shift the ratio of benefits to harms is to focus on men at highest risk, who have more to benefit than average. Neither family history nor any of the currently identified genomic markers offer sufficient risk stratification for practical use. However, there is considerable evidence that the levels of PSA in blood are strongly prognostic of the long-term risk of aggressive prostate cancer. Specifically, it is difficult to justify continuing to screen men age 60 or older if they have a PSA less than 1 or 2 ng/ml; for men 45 – 60, intervals between PSA tests can be based on PSA levels, with 2 to 4 year re-testing interval for men with PSA of 1 ng/ml or higher, and tests every 6 to 8 years for men with PSA < 1 ng/ml. Men with the top 10% of PSAs at a young age (PSA ~1.5 ng / ml or higher below 50) are at particularly high risk and should be subject to intensive monitoring.
prostatic neoplasms; early detection of cancer; prostate-specific antigen
Prostate-specific antigen (PSA) dynamics have been proposed to predict outcome in men with prostate cancer. We assessed the value of PSA velocity (PSAV) and doubling time (PSADT) for predicting prostate-cancer–specific mortality (PCSM) in men with clinically localized prostate cancer undergoing conservative management or early hormonal therapy. From 1990 to 1996, 2333 patients were identified, of whom 594 had two or more PSA values before diagnosis. We examined 12 definitions for PSADT and 10 for PSAV. Because each definition required PSA measurements at particular intervals, the number of patients eligible for each definition varied from 40 to 594 and number of events from 10 to 119. Four PSAV definitions, but no PSADT, were significantly associated with PCSM after adjustment for PSA in multivariable Cox proportional hazards regression. All 4 could be calculated only for a proportion of events, and the enhancements in predictive accuracy associated with PSAV had very wide confidence intervals. There was no clear benefit of PSAV in men with low PSA and Gleason grade 6 or less. Although evidence that certain PSAV definitions help predict PCSM in the cohort exist, the value of incorporating PSAV in predictive models to assist in determining eligibility for conservative management is, at best, uncertain.
prostate-specific antigen; prostate-specific antigen velocity; prostate-specific antigen doubling time; watchful waiting; prediction
Prostate specific antigen (PSA) is widely used for prostate cancer screening but its levels are influenced by many non cancer-related factors. The goal of the study is to estimate the effect of genetic variants on PSA levels.
We evaluated the association of SNPs that were reported to be associated with prostate cancer risk in recent genome-wide association studies with plasma PSA levels in a Swedish study population, including 1,722 control subjects without a diagnosis of prostate cancer.
Of the 16 SNPs analyzed in control subjects, significant associations with PSA levels (P≤0.05) were found for six SNPs. These six SNPs had a cumulative effect on PSA levels; the mean PSA levels in men were almost twofold increased across increasing quintile of number of PSA associated alleles, P-trend=3.4×10−14. In this Swedish study population risk allele frequencies were similar among T1c case patients (cancer detected by elevated PSA levels alone) as compared to T2 and above prostate cancer case patients.
Results from this study may have two important clinical implications. The cumulative effect of six SNPs on PSA levels suggests genetic-specific PSA cutoff values may be used to improve the discriminatory performance of this test for prostate cancer; and the dual associations of these SNPs with PSA levels and prostate cancer risk raise a concern that some of reported prostate cancer risk-associated SNPs may be confounded by the prevalent use of PSA screening.
genetic; bias; KLK3
The National Comprehensive Cancer Network and American Urological Association guidelines on early detection of prostate cancer recommend biopsy on the basis of high prostate-specific antigen (PSA) velocity, even in the absence of other indications such as an elevated PSA or a positive digital rectal exam (DRE).
To evaluate the current guideline, we compared the area under the curve of a multivariable model for prostate cancer including age, PSA, DRE, family history, and prior biopsy, with and without PSA velocity, in 5519 men undergoing biopsy, regardless of clinical indication, in the control arm of the Prostate Cancer Prevention Trial. We also evaluated the clinical implications of using PSA velocity cut points to determine biopsy in men with low PSA and negative DRE in terms of additional cancers found and unnecessary biopsies conducted. All statistical tests were two-sided.
Incorporation of PSA velocity led to a very small increase in area under the curve from 0.702 to 0.709. Improvements in predictive accuracy were smaller for the endpoints of high-grade cancer (Gleason score of 7 or greater) and clinically significant cancer (Epstein criteria). Biopsying men with high PSA velocity but no other indication would lead to a large number of additional biopsies, with close to one in seven men being biopsied. PSA cut points with a comparable specificity to PSA velocity cut points had a higher sensitivity (23% vs 19%), particularly for high-grade (41% vs 25%) and clinically significant (32% vs 22%) disease. These findings were robust to the method of calculating PSA velocity.
We found no evidence to support the recommendation that men with high PSA velocity should be biopsied in the absence of other indications; this measure should not be included in practice guidelines.
Prostate-specific antigen (PSA) has modest specificity for prostate cancer. A panel of four kallikrein markers (total, free, and intact PSA and kallikrein-related peptidase 2) is a highly accurate predictor of biopsy outcome. The clinical significance of biopsy-detectable cancers in men classified as low risk by this panel remains unclear.
The Malmö Diet and Cancer study is a population-based cohort of 11,063 Swedish men aged 45–73 providing a blood sample at baseline during 1991–1996. The Swedish Cancer Registry was used to identify 943men diagnosed with prostate cancer by 12/31/2006. PSA-testing was low. We assessed the predictive accuracy of our published statistical model to predict subsequent prostate cancer diagnosis in men with total PSA ≥3.0ng/mlat baseline.
Compared to total PSA and age, the full kallikrein panel enhanced the predictive accuracy for clinically diagnosed prostate cancer (concordance index 0.65 vs 0.75; p<0.001). For every 1000 men with total PSA≥3 ng/ml at baseline, the model would classify as high risk131/152 (86%)of the cancer cases diagnosed clinically within five years; 421men would be classified as low risk by the panel and recommended against biopsy. Of these, only 2would be diagnosed with advanced prostate cancer (clinical T3–T4 or metastases) within five years.
Men with PSA≥3 ng/ml but defined as low risk by the panel of four kallikrein markers are unlikely to develop incurable prostate cancer.
Use of the panel to determine referral to biopsy could substantially reduce the number of unnecessary prostate biopsies.
Prostate cancer; screening; PSA; prediction
To compare the predictive performance and potential clinical usefulness of risk calculators of the European Randomized Study of Screening for Prostate Cancer (ERSPC RC) with and without information on prostate volume.
We studied 6 cohorts (5 European and 1 US) with a total of 15,300 men, all biopsied and with pre-biopsy TRUS measurements of prostate volume. Volume was categorized into 3 categories (25, 40, and 60 cc), to reflect use of digital rectal examination (DRE) for volume assessment. Risks of prostate cancer were calculated according to a ERSPC DRE-based RC (including PSA, DRE, prior biopsy, and prostate volume) and a PSA + DRE model (including PSA, DRE, and prior biopsy). Missing data on prostate volume were completed by single imputation. Risk predictions were evaluated with respect to calibration (graphically), discrimination (AUC curve), and clinical usefulness (net benefit, graphically assessed in decision curves).
The AUCs of the ERSPC DRE-based RC ranged from 0.61 to 0.77 and were substantially larger than the AUCs of a model based on only PSA + DRE (ranging from 0.56 to 0.72) in each of the 6 cohorts. The ERSPC DRE-based RC provided net benefit over performing a prostate biopsy on the basis of PSA and DRE outcome in five of the six cohorts.
Identifying men at increased risk for having a biopsy detectable prostate cancer should consider multiple factors, including an estimate of prostate volume.
PSA; Risk; Prostate cancer; Prostate volume; Calibration; Net benefit
We have previously identified a locus on human chromosome 20q13.1, encompassing related genes of postulated WFDC-type protease inhibitors and semen coagulum proteins. Three of the genes with WFDC motif also coded for the Kunitz-type protease inhibitor motif. In this report, we have reinvestigated the locus for homologous genes encoding Kunitz motif only. The identified genes have been analyzed with respect to structure, expression and function.
We identified three novel genes; SPINT3, SPINT4 and SPINT5, and the structure of their transcripts were determined by sequencing of DNA generated by rapid amplification of cDNA ends. Each gene encodes a Kunitz domain preceded by a typical signal peptide sequence, which indicates that the proteins of 7.6, 8.7, and 9.7 kDa are secreted. Analysis of transcripts in 26 tissues showed that the genes predominantly are expressed in the epididymis. The recombinantly produced proteins could not inhibit the amidolytic activity of trypsin, chymotrypsin, plasmin, thrombin, coagulation factor Xa, elastase, urokinase and prostate specific antigen, whereas similarly made bovine pancreatic trypsin inhibitor (BPTI) had the same bioactivity as the protein isolated from bovine pancreas.
The similar organization, chromosomal location and site of expression, suggests that the novel genes are homologous with the genes of WFDC-type protease inhibitors and semen coagulum proteins, despite the lack of similarity in primary structure of their protein products. Their restricted expression to the epididymis suggests that they could be important for male reproduction. The recombinantly produced proteins are presumably bioactive, as demonstrated with similarly made BPTI, but may have a narrower spectrum of inhibition, as indicated by the lacking activity against eight proteases with differing specificity. Another possibility is that they have lost the protease inhibiting properties, which is typical of Kunitz domains, in favor of hitherto unknown functions.
Beta-microseminoprotein (MSP) is one of the three most abundantly secreted proteins of the prostate, and has been suggested as a biomarker for prostate cancer risk. A common variant, rs10993994, in the 5’ region of the gene which encodes MSP (MSMB), has recently been identified as a risk factor for prostate cancer.
We examined the association between rs10993994 genotype and MSP levels in a sample of 500 prostate cancer-free men from four racial/ethnic populations in the Multiethnic Cohort (European Americans, African Americans, Latinos, and Japanese Americans). Generalized linear models were used to estimate the association between rs10993994 genotype and MSP levels.
We observed robust associations between rs10994994 genotype and MSP levels in each racial/ethnic population (all P<10−8) with carriers of the C allele having lower geometric mean MSP levels (ng/mL) (CC/CT/TT genotypes: European Americans, 28.8/20.9/10.0; African Americans, 29.0/21.9/10.9; Latinos, 29.2/17.1/8.3; and Japanese Americans 25.8/16.4/6.7). We estimated the variant accounts for 30–50% of the variation in MSP levels in each population. We also observed significant differences in MSP levels between populations (P=3.5×10−6), with MSP levels observed to be highest in African Americans and lowest in Japanese Americans.
Rs10993994 genotype is strongly associated with plasma MSP levels in multiple racial/ethnic populations.
This supports the hypothesis that rs10993994 may be the biologically functional allele.
MSMB; beta-microseminoprotein; prostate; genetic; multiethnic
The relationship between prostate specific antigen (PSA) level and prostate cancer risk remains subject to fundamental disagreements. We hypothesize that the risk of prostate cancer on biopsy for a given PSA level is affected by identifiable characteristics of the cohort under study.
We used data from 5 European and 3 US cohorts of men undergoing biopsy for prostate cancer; six were population-based studies and two were clinical cohorts. The association between PSA and prostate cancer was calculated separately for each cohort using locally-weighted scatterplot smoothing.
The final data set included 25,772 biopsies and 8,503 cancers. There were gross disparities between cohorts with respect to both the prostate cancer risk at a given PSA level and the shape of the risk curve. These disparities were associated with identifiable differences between cohorts: for a given PSA level, a greater number of biopsy cores increased risk of cancer (odds ratio for >6 vs. 6 core biopsy 1.35; 95% C.I. 1.18, 1.54; p<0.0005); recent screening led to a smaller increase in risk per unit change in PSA (p=0.001 for interaction term) and US cohorts had higher risk than the European cohorts (2.14; 95% C.I. 1.99, 2.30; p<0.0005).
Our results suggest that the relationship between PSA and risk of a positive prostate biopsy varies, both in terms of the probability of prostate cancer at a given PSA value and the shape of the risk curve. This poses challenges to the use of PSA-driven algorithms to determine whether biopsy is indicated.
prostate cancer; PSA; prediction; multicenter studies; screening
rs10993994, a single nucleotide polymorphism (SNP) at the genetic locus encoding ß-microseminoprotein (β-MSP), is associated with both prostate cancer risk and levels of blood prostate-specific antigen (PSA), a biomarker used in prostate cancer screening. Therefore, we wished to determine the association between SNPs at MSMB, the gene encoding β-MSP, and levels of the prostate-produced biomarkers β-MSP, PSA, and human kallikrein 2 (hK2) in blood and semen.
Blood and semen from 304 healthy young Swedish men (aged 18-21) were assayed for β-MSP, PSA and hK2. SNPs around MSMB were genotyped from matched DNA and analyzed for quantitative association with biomarker levels. Empirical p-values were multiple test corrected and independence of each SNP’s effect was determined.
rs10993994 is significantly associated with blood and semen levels of β-MSP (both p<1.0×10−7) and PSA (p=0.00014 and p=0.0019), and semen levels of hK2 (p=0.00027). Additional copies of the prostate cancer risk allele resulted in lower β-MSP but higher PSA levels, and singly explained 23% and 5% of the variation seen in semen β-MSP and PSA. Additional SNPs at MSMB are associated with β-MSP and PSA independently of rs10993994.
SNPs at MSMB correlate with physiological variation in β-MSP and PSA levels in the blood and semen of healthy young Swedish men. In particular, rs10993994 has a strong effect on β-MSP levels.
Our results suggest a mechanism by which rs10993994 may predispose to prostate cancer and raise the possibility that genetic variation may need to be considered in interpreting levels of these biomarkers.
PSA; beta-MSP; prostate biomarker; rs10993994; microseminoprotein beta; PSP94; hK2
We have developed a statistical prediction model for prostate cancer based on four kallikrein markers in blood: total, free, and intact prostate specific antigen (PSA) and kallikrein-related peptidase 2 (hK2). Although this model accurately predicts the result of biopsy in unscreened men, its properties for men with a history of PSA screening have not been fully characterized.
1501 previously screened men with elevated PSA underwent initial biopsy during rounds 2 and 3 of the European Randomized Study of Prostate Cancer Screening, Rotterdam, with 388 cancers diagnosed. Biomarker levels were measured in serum samples taken before biopsy. The prediction model developed on the unscreened cohort was then applied and predictions compared to biopsy outcome.
The previously developed four-kallikrein prediction model had much higher predictive accuracy than PSA and age alone (area-under-the-curve of 0.711 vs. 0.585 and 0.713 vs. 0.557 with and without digital rectal exam, respectively; both p<0.001). Similar statistically significant enhancements were seen for high-grade cancer. Applying the model with a cut-off of 20% cancer risk as the criterion for biopsy would reduce the biopsy rate by 362 for every 1000 men with elevated PSA. Although diagnosis would be delayed for 47 cancers, these would be predominately low stage and low grade (83% Gleason 6 T1c).
A panel of four kallikreins can help predict the result of initial biopsy in previously screened men with elevated PSA. Use of a statistical model based on the panel would substantially decrease rates of unnecessary biopsy.
prostate cancer; biomarkers; predictive value of tests; prostate-specific antigen; cancer screening
Elevated cystatin C in blood reflects impaired glomerular filtration rate (GFR), but current cystatin C assays, based on polyclonal antibodies and immunoturbidimetric or nephelometric detection, have several limitations. We evaluated a new immunoassay based on monoclonal antibodies in samples from patients with and without chronic kidney disease (CKD).
The study enrolled 170 men without known CKD (Group A) and 104 men with CKD (Group B). All patients were assessed with iohexol clearance, plasma creatinine and plasma cystatin C by a conventional particle-enhanced immunoturbidimetric assay (PETIA) and by the new double monoclonal assay. In Group A, three serial blood draws were performed at median intervals of 4 h and 12 days between samples, to also allow assessments of the variability in cystatin C values with the new assay. Concordance correlation coefficients and the 95% limits of agreement were used to estimate the agreement of reciprocal cystatin C and reciprocal creatinine with iohexol clearance.
Median iohexol clearance (mL/min/1.73 m2) was 81 [interquartile range (IQR) 70, 92] in Group A and 23 (IQR 16, 34) in Group B. The concordance correlation with GFR for the new cystatin C assay compared to the established assay was similar in Group A (0.441 versus 0.465) but higher in Group B (0.680 versus 0.593). Cystatin C measured by both assays exhibited closer agreement with GFR than creatinine. The agreement between the two cystatin C assays was high, with concordance correlations of 0.815 in Group A and 0.935 in Group B. Compared to the conventional assay, the new assay tended to yield lower values of cystatin C at the low end of the range in Group A. The new cystatin C assay exhibited small intraindividual variability across serial samples (coefficient of variation ≤6%).
In this first clinical evaluation, the new cystatin C assay performed similarly to the established PETIA in patients with normal GFR and better in patients with CKD. The new assay may offer an alternative to current commercial assays to detect and monitor impaired kidney function.
creatinine; cystatin C; glomerular filtration rate; iohexol clearance; renal function
Risk models to predict prostate cancer on biopsy, whether they include only prostate-specific antigen (PSA) or other markers, are intended for use in all men of screening age. Yet the association between PSA and cancer likely depends on a man’s recent screening history.
To examine the effect of prior screening on prostate cancer risk prediction using a previously reported four-kallikrein panel: total, free, and intact PSA, and kallikrein-related peptidase 2 (hK2). The study cohort comprised 1241 men in Gothenburg, Sweden, undergoing biopsy for elevated PSA during their second or later visit for the European Randomized study of Screening for Prostate Cancer. We calculated the predictive accuracy of a four-kallikrein panel.
Total PSA was not predictive of prostate cancer. A previously published four-kallikrein model increased predictive accuracy compared to total PSA and age alone (area-under-the-curve [AUC] 0.66 vs. 0.51; p<0.001), but was poorly calibrated and missed many cancers. A model developed with recently screened men gave important improvements in discrimination (AUC 0.67 vs. 0.56; p<0.001). Use of this model would reduce the number of biopsies by 413 per 1000 men with elevated PSA, miss 60 of 216 low-grade (Gleason ≤6) cancers, but miss only 1 of 43 high-grade cancers.
Prior participation in PSA-screening dramatically changes the performance of statistical models predicting biopsy outcome. A four-kallikrein panel can predict prostate cancer in men with a recent screening history, providing independent replication that multiple kallikrein-forms contribute important diagnostic value in men with elevated PSA.
prostate cancer; screening; prostate specific antigen; kallikreins; molecular markers
We previously reported that a panel of four kallikrein forms in blood—total, free, and intact prostate-specific antigen (PSA) and kallikrein-related peptidase 2 (hK2)—can reduce unnecessary biopsy in previously unscreened men with elevated total PSA. We aimed to replicate our findings in a large, independent, representative, population-based cohort.
Patients and Methods
The study cohort included 2,914 previously unscreened men undergoing biopsy as a result of elevated PSA (≥ 3 ng/mL) in the European Randomized Study of Screening for Prostate Cancer, Rotterdam, with 807 prostate cancers (28%) detected. The cohort was randomly divided 1:3 into a training and validation set. Levels of kallikrein markers were compared with biopsy outcome.
Addition of free PSA, intact PSA, and hK2 to a model containing total PSA and age improved the area under the curve from 0.64 to 0.76 and 0.70 to 0.78 for models without and with digital rectal examination results, respectively (P < .001 for both). Application of the panel to 1,000 men with elevated PSA would reduce the number of biopsies by 513 and miss 54 of 177 low-grade cancers and 12 of 100 high-grade cancers. Findings were robust to sensitivity analysis.
We have replicated our previously published finding that a panel of four kallikreins can predict the result of biopsy for prostate cancer in men with elevated PSA. Use of this panel would dramatically reduce biopsy rates. A small number of men with cancer would be advised against immediate biopsy, but these men would have predominately low-stage, low-grade disease.