Multiparametric magnetic resonance imaging-ultrasound fusion-guided prostate biopsy: role in diagnosis and management of prostatic cancer.

We have read with great interest the review article by Sonn et al. [1] in the November 2013 issue of Urologic Oncology. We agree with the article content, but we believe that the role of multiparametric magnetic resonance imaging-ultrasound (mpMRI-US) fusion-guided prostate biopsy, in the various steps of prostate cancer (PCa) diagnosis and management, should be further outlined. The PCa aggressiveness stratification includes 3 groups of different risk: low, intermediate, and high risk. The most common clinical data used to define low-risk PCa include the following: Gleason score ≤6 (no disease pattern 4 or 5), prostate-specific antigen (PSA) level <10 ng/ml, clinical T1 or T2a clinical category disease, PSA kinetics (stable) before diagnosis, PSA density<0.15 ng/ml/cm3, percentage of positive cores at biopsy <33%, and the extent of cancer in any cores <50% [2]. Active surveillance (AS) is a new strategy that aims to individualize therapy by selecting only those patients with significant cancers for curative therapy, particularly those with low risk of PCa. AS includes 4 key components: identification of appropriate patients, patient education and reassurance, close monitoring over time (with serial PSA measurements, periodic biopsy, and imaging studies), and appropriate therapy for patients whose disease is reclassified as higher risk [3]. AS follow-up includes (1) PSA evaluation and digital rectal examination every 3 months for 2 years and then every 6 months (assuming a stable PSA), (2) confirmatory 10- to 12-core biopsy within the first year, including those of the anterolateral horn, (3) repeat biopsy every 3 to 5 years until the age of 80 years, and (4) MRI at baseline, or for borderline PSA kinetics or pathology, or both [2]. The published experience with AS of more than 2,000 patients has demonstrated that approximately one-third of patients with low-risk PCa are reclassified as higher risk for progression and are treated [3], [4], [5], [6], [7], [8] and [9]. In the intermediate time frame (5–15 y), PCa mortality is exceptionally low. Biopsy sampling error is a significant limitation of AS. The anterolateral horn is a common site for disease missed on routine biopsies. Lawrentschuk and Fleshner [10], in some patients (perhaps 20%) diagnosed with favorable risk and harboring large, high-grade cancers, identified a subset of patients either having anterior-predominant tumors with negative findings on biopsy or low-volume disease and who are on AS and should be considered for MRI and further biopsy, as their pathology might be aggressive. The authors used the term “prostatic evasive anterior tumors” and demonstrated that the use of mpMRI may increase awareness of anterior disease, facilitate surgical planning, and add information to other treatment options, including AS. Although not widely implemented, current studies report up to an 86% sensitivity and a 94% specificity of mpMRI in diagnosis of PCa, improved correlation with pathological tumor volume and decreased upgrading with anterior disease [11] and [12]. MpMRI of 3.0 T can be used not only for patients with high PSA levels suggestive of PCa and previously negative findings on biopsies to undergo prostate biopsy but also as the first approach for tumor detection before biopsy [13], [14], [15] and [16]. mpMRI-US fusion allows the information to be used to direct needle biopsy under US guidance, with improvement of prostate biopsy in an office-based procedure [1]. The European Society of Urogenital Radiology Prostate Imaging Reporting and Data System reported that this scoring system using multiparametric 3.0-T MRI is beneficial to indicate the likelihood of PCa of suspicious lesions on mpMRI and valuable to identify locations to be targeted with biopsy [17]. In the review by Sonn et al. [1], mpMRI is indicated to be more expensive than conventional transrectal US (TRUS) biopsy and time consuming, it requires MRI-compatible equipment and often a general anesthetic, it is not available in most hospitals, and a radiologist experienced in MRI is required. The authors do not specify which MRI images to use to achieve fusion of MRI with US to guide biopsy. In our experience, using 3.0-T pelvic phased-array with coil, in the perspective to use the mpMRI-US fusion to direct biopsy needles under US guidance as alternative to transrectal US-guided biopsy, we consider diffusion-weighted imaging (DWI) and apparent diffusion coefficient maps (ADC) as the most accurate to detect suspected areas of PCa. Unfortunately, the DWI suffers from low signal-to-noise ratio, spatial resolution, or image quality. As a consequence, before fusing the US images with corresponding MR images representative of suspected foci of PCa, the choice of DWI images to fuse with the corresponding 3D T2-weighed, or 3DCE images is required. In conclusion, the mpMRI-US fusion-guided prostate biopsy is emerging as a potential leading imaging tool for the detection of significant PCa. It can be used as the initial diagnostic approach in the detection of intraprostatic foci suspected for PCa, particularly for prostatic evasive anterior tumors, and in the follow-up of patients with low-risk PCa with AS. Guidelines for diagnosis and management of PCa should include indications such as the role of mpMRI in staging purposes and the need of accurate standardization.