Platinum Priority – Prostate CancerEditorial by Scott Eggener on pp. 54–55 of this issueUrine TMPRSS2:ERG Plus PCA3 for Individualized Prostate Cancer Risk Assessment
Introduction
Approximately 1 million men undergo prostate biopsy each year in the United States, most for elevated serum prostate-specific antigen (PSA or KLK3). Serum PSA's lack of prostate cancer (PCa) specificity, the unclear benefits of PSA screening for reducing PCa deaths, and the harms of overdiagnosing indolent disease have called PSA screening into question [1], [2], [3]. Although aggressive PCa-specific biomarkers may eventually replace serum PSA, at present, methods to individualize management of elevated PSA are needed. Such approaches include multivariate risk models, such as the Prostate Cancer Prevention Trial risk calculator (PCPTrc), which includes serum PSA and clinical factors [4], [5], [6]. Likewise, multiple PSA derivatives and other related kallikreins have been advanced as early detection biomarkers, including free PSA and [−2]proPSA (both of which are incorporated, with total PSA, in the Prostate Health Index [PHI]), with free PSA and PHI approved by the US Food and Drug Administration (FDA) for PCa risk estimation in men with serum PSA of 4–10 ng/ml [7], [8], [9]. Similarly, a panel of free and total PSA, single-chain intact PSA, and a related kallikrein (KLK2) outperforms serum PSA alone for predicting PCa on biopsy, and a test incorporating these kallikreins along with clinical parameters (4Kscore) is available [7], [9].
An alternative to using tissue-specific biomarkers, such as serum PSA and other kallikreins, for predicting the presence of PCa is to utilize PCa-specific biomarkers. Prostate cancer antigen 3 (PCA3; a noncoding RNA) and TMPRSS2:ERG (T2:ERG) gene fusions are the most advanced PCa-specific early detection biomarkers [10], [11], [12], [13]. In tissues, both biomarkers show markedly improved PCa specificity compared with PSA or derivatives or related kallikreins [12], [14], [15]. In addition, both PCA3 and T2:ERG transcripts are detectable and quantifiable in urine collected after digital rectal examination (DRE) [10], [11], [12], [13]. The Progensa PCA3 test (Hologic Inc, Bedford, MA, USA), which reports a quantitative PCA3 score using a transcription-mediated amplification (TMA) assay, has been extensively studied as a urine-based PCa biomarker [11], [12], [13] and is FDA approved for estimating PCa risk following a negative biopsy.
Previously, we reported the development and application of a clinical-grade TMA assay for quantifying T2:ERG messenger RNA (mRNA), which generates a T2:ERG score by normalizing urine T2:ERG mRNA to urine PSA mRNA (to control for prostate cell and mRNA abundance) [16]. This assay is based on the same technology as the Progensa PCA3 test and can be performed on the same post-DRE whole urine sample. Previously, we applied initial T2:ERG TMA assay versions to post-DRE whole urine from 1312 men presenting for biopsy or prostatectomy at multiple centers [16]. More recently, we and others have evaluated the performance of a final clinical-grade T2:ERG TMA assay [17], [18], [19], [20]. In this study, we evaluated pretrained multivariate regression models combining urine T2:ERG and/or PCA3 scores with serum PSA (or the PCPTrc) in a large independent validation cohort to develop methods for individualized PCa risk estimates.
Section snippets
Patients
The regression models were developed in a training cohort and validated in an independent cohort. For the training cohort, post-DRE urine was prospectively collected from 733 patients presenting for diagnostic prostate biopsy at three US academic institutions and assessed for urine T2:ERG and PCA3 scores at the University of Michigan Health System (training cohort), predominantly as part of an Early Detection Research Network (EDRN) biopsy cohort [21], using standardized protocols. For the
Development of logistic regression models incorporating urine T2:ERG and PCA3 scores
The multivariable logistic regression models evaluated in this study were developed using a 733-specimen training cohort. Of the 711 samples (97%) that were informative for both urine T2:ERG and PCA3 scores (sufficient urine PSA [10 000 copies per milliliter] to ensure adequate prostatic-derived RNA), 689 samples were collected as part of an EDRN protocol [21] and were from men without PCa presenting for biopsy. The remaining 22 informative samples were collected in the same manner from men with
Discussion
We developed and validated risk models, termed MiPS, combining urine T2:ERG and PCA3 scores with serum PSA or the PCPTrc for predicting the presence of PCa (or high-grade cancer) on biopsy. T2:ERG and PCA3 represent the most advanced urine biomarkers for PCa [11], [12]. The Progensa PCA3 test (used in this study) is FDA approved in the setting of a prior negative biopsy, and recent reports support utility in the initial biopsy setting [10], [11], [12], [13], [21], [23]. Of note, in our large
Conclusions
In summary, we reported validated individualized risk models (MiPS) incorporating serum PSA (or the PCPTrc) and urine T2:ERG and PCA3 scores for predicting PCa and high-grade PCa risk on needle biopsy. By AUC, assessment of unnecessary biopsies avoided, and DCA, MiPS models significantly outperformed serum PSA (or PCPTrc)-based strategies, supporting the use of the MiPS test as a decision-making aide for men (and their physicians) concerned about serum PSA test results, particularly in the
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