Platinum Priority – Prostate CancerEditorial by Mark Emberton on pp. 720–721 of this issueMagnetic Resonance Imaging/Ultrasound–Fusion Biopsy Significantly Upgrades Prostate Cancer Versus Systematic 12-core Transrectal Ultrasound Biopsy
Introduction
Pathologic grading of prostate cancer (PCa) based on biopsy Gleason score (bGS) plays an important role in clinical decision making. Unfortunately, a number of studies have identified a poor correlation between the Gleason score identified on prostate biopsy and that found in the prostatectomy specimen, with rates of Gleason score upgrading between 21% and 54% [1], [2], [3]. Cookson and colleagues have also reported a discrepancy of two or more grades in 26% of cases [4]. The challenge is that surgical-specimen Gleason scores are obtained too late (after the surgery) to influence decision making, algorithms, and triage that involve surgery.
Multiparametric prostate magnetic resonance imaging (MP-MRI) has emerged as an accurate modality in detecting PCa. Lesions identified on MP-MRI correlate with tumor location on radical prostatectomy specimens [5]. A similar study found that the level of radiologic suspicion based on MP-MRI findings correlates with the D’Amico risk stratification [6].
The ability to detect, delineate, and measure PCa on magnetic resonance imaging (MRI) has led to the development of three MRI-guided prostate biopsy methods: cognitive fusion, direct MRI-guided biopsy, and several methods of MRI/ultrasound (MRI/US)-fusion-guided biopsy [7]. Cognitive fusion involves an estimation of the location of the lesion on the part of the transrectal ultrasound (TRUS) operator and varies greatly with expertise. Direct MRI-guided biopsy is time consuming and resource costly. In contrast, MRI/US-fusion-guided biopsy is an outpatient procedure, in which prebiopsy MRI of the prostate is segmented, registered, and fused with real-time ultrasound using electromagnetic tracking or mechanical-arm navigation and a digital overlay. This method integrates well with current workflow patterns of TRUS-guided biopsy yet provides a platform for a targeted approach to prostate biopsy based on MRI-identified targets and lesions [8]. MRI/US-fusion-guided biopsy has the potential to offer improved diagnostic information over 12-core biopsy alone. To study whether MRI/US fusion results in more accurate biopsies, the correlation was assessed between the Gleason scores detected on MRI/US-fusion biopsy and those found on a standard 12-core TRUS biopsy performed during the same biopsy session.
Section snippets
Study population
Subjects were enrolled in a prospective trial assessing MRI/US-fusion-guided prostate biopsy with electromagnetic tracking at the US National Cancer Institute and the US National Institutes of Health between August 2007 and August 2012 (ClinicalTrials.gov identifier: NCT00102544). Institutional review board approval was obtained and all subjects provided written informed consent. During the study period, a total of 671 MRI/US-fusion-guided prostate biopsies were performed, including 89 patients
Results
Patient demographics of the study cohort are shown in Table 1. The mean age of the patient population was 61.3 yr and mean prebiopsy PSA level was 9.9 ng/ml. The mean number of targeted biopsies per patient was 5.7, and, accordingly, the mean total number of biopsies including the standard 12-cores was 17.7. Abnormal findings on TRUS were observed in 79 (14%) of subjects.
The rate of Gleason score upgrading with targeted MRI/US-fusion-guided prostate biopsy was compared with standard 12-core
Discussion
There has been considerable concern regarding overdiagnosis and subsequent overtreatment of men with clinically indolent PCa; thus, better characterization of PCa is highly desirable [14]. MRI/US-fusion-guided, targeted biopsies may potentially offer such an improvement [15]. An initial cohort in this same clinical trial previously demonstrated that MRI/US-fusion-guided targeted biopsy increased cancer detection rates significantly compared with standard 12-core TRUS biopsy alone, especially in
Conclusions
In this study, the rate of Gleason score upgrading with MRI/US-fusion-guided targeted biopsies was examined and a 32% rate of increased Gleason score was found when compared with standard extended 12-core biopsy alone. The converse relationship was also examined of 12-core biopsies as an adjunct to targeted biopsies alone and found a 26% rate of Gleason score upgrading. Most of these cases were due to new bGS 6 tumors that were detected; however, seven patients were upgraded to bGS ≥4 + 3
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