Prebiopsy Multiparametric Magnetic Resonance Imaging Research Articles

Multiparametric Prostate Magnetic Resonance Imaging and Cognitively Targeted Transperineal Biopsy in Patients With Previous Abdominoperineal Resection and Suspicion of Prostate Cancer

To report our experience with a combination of prostate magnetic resonance imaging (MRI) and transperineal ultrasound biopsy for evaluating the prostate in patients with elevated prostate-specific antigen (PSA) who have previously undergone abdominoperineal resection (APR). We reviewed the records of 11 patients with a history of APR and clinical suspicion of prostate cancer due to elevated PSA levels over a 5-year period. All patients underwent multiparametric MRI at our institution prior to biopsy. MR diagnoses were validated either by transperineal ultrasound biopsy (Likert 3-5) guided by visual registration or clinical follow-up >6 months (Likert 1-2). All 7 cases with highly suspicious lesions (Likert 4-5) on MRI demonstrated cancer-1 case of Gleason 3 + 3 and 6 cases of Gleason ≥3 + 4 disease. Two cases with Likert 3 MR lesions revealed benign tissue upon biopsy. Two patients with no suspicious lesions on MRI were followed-up clinically, with PSA levels remaining stable over a mean period of 17.5 months (range 7-28 months). The use of prebiopsy multiparametric prostate MRI and subsequent cognitively targeted transperineal biopsy guided by visual registration can aid in the diagnostic pathway of patients with APR and a suspicion of prostate cancer.

Predictive value of negative 3T multiparametric magnetic resonance imaging of the prostate on 12-core biopsy results.

To evaluate the cancer detection rates for men undergoing 12-core systematic prostate biopsy with negative prebiopsy multiparametric magnetic resonance imaging (mpMRI) results. Clinical data from consecutive men undergoing prostate biopsy who had undergone prebiopsy 3T mpMRI from December 2011 to August 2014 were reviewed from an institutional review board-approved prospective database. Men with negative prebiospy mpMRI results (negMRI) before biopsy were identified for the present analysis. Clinical features, cancer detection rates and negative predictive values were summarized. Seventy five men with negMRI underwent systematic 12-core biopsy during the study period. In the entire cohort, men with no previous biopsy, men with previously negative biopsy and men enrolled in active surveillance protocols, the overall cancer detection rates were 18.7, 13.8, 8.0 and 38.1%, respectively, and the detection rates for Gleason score (GS) ≥7 cancer were 1.3, 0, 4.0 and 0%, respectively. The NPVs for all cancers were 81.3, 86.2, 92.0, and 61.9, and for GS ≥7 cancer they were 98.7, 100, 96.0 and 100%, respectively. A negative prebiopsy mpMRI confers an overall NPV of 82% on 12-core biopsy for all cancer and 98% for GS ≥7 cancer. Based on biopsy indication, these findings assist in prebiopsy risk stratification for detection of high-risk disease and may provide guidance in the decision to pursue biopsy.

Is Prebiopsy MRI Good Enough to Avoid Prostate Biopsy? A Cohort Study Over a 1-Year Period

IntroductionPrebiopsy multiparametric magnetic resonance imaging (MRI) is increasingly used in clinical practice to detect clinically significant prostate cancer, although its role is controversial. We audited the accuracy of prebiopsy MRI for men clinically suspected to have prostate cancer who underwent initial transrectal ultrasound (TRUS) biopsy at our institution. Patients and MethodsAll patients who had a prebiopsy prostate MRI and initial TRUS prostate biopsy from January 1, 2013 to December 31, 2013 were included in the study. Prostate MRI was performed using a 1.5-T machine with T2 and diffusion weighted imaging axial phase. TRUS prostate biopsy was performed using a monoplane ultrasound machine. Systematic 12-core prostate biopsies were taken with a Tru-Cut biopsy needle from the apex, middle, and base of the left and right lobe. ResultsOne hundred seventy-three patients met the inclusion criteria; 128 (74.4%) patients had a lesion detected on MRI and 114 (66.3%) patients had a positive biopsy. The sensitivity of MRI for significant prostate cancer on TRUS biopsy of the prostate was 83.5%, specificity was 35.2%, positive predictive value was 55%, and negative predictive value was 68.9%. A positive MRI scan was significantly associated with significant prostate cancer diagnosis, and higher National Comprehensive Cancer Network (NCCN) risk classification (P ≤ .001). MRI detected 62 of 63 NCCN high-risk and 18 of 18 Gleason score 8 to 10 cases. ConclusionThe sensitivity and specificity of MRI appears insufficient to avoid TRUS biopsy in all men clinically suspected to have prostate cancer. Standardized MRI reporting and robust prospective studies are needed to define the role of prebiopsy MRI in this setting. For patients at risk of complications from biopsy, a negative MRI scan might be used to exclude high-risk disease.

Relationship Between Prebiopsy Multiparametric Magnetic Resonance Imaging (MRI), Biopsy Indication, and MRI-ultrasound Fusion–targeted Prostate Biopsy Outcomes

BackgroundIncreasing evidence supports the use of magnetic resonance imaging (MRI)-ultrasound fusion–targeted prostate biopsy (MRF-TB) to improve the detection of clinically significant prostate cancer (PCa) while limiting detection of indolent disease compared to systematic 12-core biopsy (SB). ObjectiveTo compare MRF-TB and SB results and investigate the relationship between biopsy outcomes and prebiopsy MRI. Design, setting, and participantsRetrospective analysis of a prospectively acquired cohort of men presenting for prostate biopsy over a 26-mo period. A total of 601 of 803 consecutively eligible men were included. InterventionsAll men were offered prebiopsy MRI and assigned a maximum MRI suspicion score (mSS). Men with an MRI abnormality underwent combined MRF-TB and SB. OutcomesDetection rates for all PCa and high-grade PCa (Gleason score [GS] ≥7) were compared using the McNemar test. Results and limitationsMRF-TB detected fewer GS 6 PCas (75 vs 121; p<0.001) and more GS ≥7 PCas (158 vs 117; p<0.001) than SB. Higher mSS was associated with higher detection of GS ≥7 PCa (p<0.001) but was not correlated with detection of GS 6 PCa. Prediction of GS ≥7 disease by mSS varied according to biopsy history. Compared to SB, MRF-TB identified more GS ≥7 PCas in men with no prior biopsy (88 vs 72; p=0.012), in men with a prior negative biopsy (28 vs 16; p=0.010), and in men with a prior cancer diagnosis (42 vs 29; p=0.043). MRF-TB detected fewer GS 6 PCas in men with no prior biopsy (32 vs 60; p<0.001) and men with prior cancer (30 vs 46; p=0.034). Limitations include the retrospective design and the potential for selection bias given a referral population. ConclusionsMRF-TB detects more high-grade PCas than SB while limiting detection of GS 6 PCa in men presenting for prostate biopsy. These findings suggest that prebiopsy multiparametric MRI and MRF-TB should be considered for all men undergoing prostate biopsy. In addition, mSS in conjunction with biopsy indications may ultimately help in identifying men at low risk of high-grade cancer for whom prostate biopsy may not be warranted. Patient summaryWe examined how magnetic resonance imaging (MRI)-targeted prostate biopsy compares to traditional systematic biopsy in detecting prostate cancer among men with suspicion of prostate cancer. We found that MRI-targeted biopsy detected more high-grade cancers than systematic biopsy, and that MRI performed before biopsy can predict the risk of high-grade cancer.

Magnetic Resonance Imaging-Ultrasound Fusion Targeted Prostate Biopsy in a Consecutive Cohort of Men with No Previous Biopsy: Reduction of Over Detection through Improved Risk Stratification

MRF-TB (magnetic resonance imaging-ultrasound fusion targeted prostate biopsy) may improve the detection of prostate cancer in men presenting for prostate biopsy. We report clinical outcomes of 12-core systematic biopsy and MRF-TB in men who presented for primary biopsy and further describe pathological characteristics of cancers detected by systematic biopsy and not by MRF-TB. Clinical outcomes of 452 consecutive men who underwent prebiopsy multiparametric magnetic resonance imaging followed by MRF-TB and systematic biopsy at our institution between June 2012 and June 2015 were captured in an institutional review board approved database. Clinical characteristics, biopsy results and magnetic resonance imaging suspicion scores were queried from the database. Prostate cancer was detected in 207 of 382 men (54.2%) with a mean±SD age of 64±8.5 years and mean±SEM prostate specific antigen 6.8±0.3 ng/ml who met study inclusion criteria. The cancer detection rate of systematic biopsy and MRF-TB was 49.2% and 43.5%, respectively (p=0.006). MRF-TB detected more Gleason score 7 or greater cancers than systematic biopsy (117 of 132 or 88.6% vs 102 of 132 or 77.3%, p=0.037). Of 41 cancers detected by systematic biopsy but not by MRF-TB 34 (82.9%) demonstrated Gleason 6 disease, and 26 (63.4%) and 34 (82.9%) were clinically insignificant by Epstein criteria and a UCSF CAPRA (University of California-San Francisco-Cancer of the Prostate Risk Assessment) score of 2 or less, respectively. In men presenting for primary prostate biopsy MRF-TB detects more high grade cancers than systematic biopsy. Most cancers detected by systematic biopsy and not by MRF-TB are at clinically low risk. Prebiopsy magnetic resonance imaging followed by MRF-TB decreases the detection of low risk cancers while significantly improving the detection and risk stratification of high grade disease.

Prebiopsy Multiparametric Magnetic Resonance Imaging for Prostate Cancer Diagnosis in Biopsy-naive Men with Suspected Prostate Cancer Based on Elevated Prostate-specific Antigen Values: Results from a Randomized Prospective Blinded Controlled Trial

BackgroundMultiparametric magnetic resonance imaging (MP-MRI) may improve the detection of clinically significant prostate cancer (PCa). ObjectiveTo compare MP-MRI transrectal ultrasound (TRUS)-fusion targeted biopsy with routine TRUS-guided random biopsy for overall and clinically significant PCa detection among patients with suspected PCa based on prostate-specific antigen (PSA) values. Design, setting, and participantsThis institutional review board-approved, single-center, prospective, randomized controlled trial (April 2011 to December 2014) included 130 biopsy-naive patients referred for prostate biopsy based on PSA values (PSA <20 ng/ml or free-to-total PSA ratio ≤0.15 and PSA <10 ng/ml). Patients were randomized 1:1 to the MP-MRI or control group. Patients in the MP-MRI group underwent prebiopsy MP-MRI followed by 10- to 12-core TRUS-guided random biopsy and cognitive MRI/TRUS fusion targeted biopsy. The control group underwent TRUS-guided random biopsy alone. InterventionMP-MRI 3-T phased-array surface coil. Outcome measurements and statistical analysisThe primary outcome was the number of patients with biopsy-proven PCa in the MP-MRI and control groups. Secondary outcome measures included the number of positive prostate biopsies and the proportion of clinically significant PCa in the MP-MRI and control groups. Between-group analyses were performed. Results and limitationsOverall, 53 and 60 patients were evaluable in the MP-MRI and control groups, respectively. The overall PCa detection rate and the clinically significant cancer detection rate were similar between the MP-MRI and control groups, respectively (64% [34 of 53] vs 57% [34 of 60]; 7.5% difference [95% confidence interval (CI), −10 to 25], p=0.5, and 55% [29 of 53] vs 45% [27 of 60]; 9.7% difference [95% CI, −8.5 to 27], p=0.8). The PCa detection rate was higher than assumed during the planning of this single-center trial. ConclusionsMP-MRI/TRUS-fusion targeted biopsy did not improve PCa detection rate compared with TRUS-guided biopsy alone in patients with suspected PCa based on PSA values. Patient summaryIn this randomized clinical trial, additional prostate magnetic resonance imaging (MRI) before prostate biopsy appeared to offer similar diagnostic accuracy compared with routine transrectal ultrasound–guided random biopsy in the diagnosis of prostate cancer. Similar numbers of cancers were detected with and without MRI. Trial registrationClinicalTrials.gov identifier: NCT01357512.

The Role of Magnetic Resonance Image Guided Prostate Biopsy in Stratifying Men for Risk of Extracapsular Extension at Radical Prostatectomy

Magnetic resonance imaging detects extracapsular extension by prostate cancer with excellent specificity but low sensitivity. This limits surgical planning, which could be modified to account for focal extracapsular extension with image directed guidance for wider excision. In this study we evaluate the performance of multiparametric magnetic resonance imaging in extracapsular extension detection and determine which preoperative variables predict extracapsular extension on final pathology when multiparametric magnetic resonance imaging predicts organ confined disease. From May 2007 to March 2014, 169 patients underwent pre-biopsy multiparametric magnetic resonance imaging, magnetic resonance imaging/transrectal ultrasound fusion guided biopsy, extended sextant 12-core biopsy and radical prostatectomy at our institution. A subset of 116 men had multiparametric magnetic resonance imaging negative for extracapsular extension and were included in the final analysis. The 116 men with multiparametric magnetic resonance imaging negative for extracapsular extension had a median age of 61 years (IQR 57-66) and a median prostate specific antigen of 5.51 ng/ml (IQR 3.91-9.07). The prevalence of extracapsular extension was 23.1% in the overall population. Sensitivity, specificity, and positive and negative predictive values of multiparametric magnetic resonance imaging for extracapsular extension were 48.7%, 73.9%, 35.9% and 82.8%, respectively. On multivariate regression analysis only patient age (p=0.002) and magnetic resonance imaging/transrectal ultrasound fusion guided biopsy Gleason score (p=0.032) were independent predictors of extracapsular extension on final radical prostatectomy pathology. Because of the low sensitivity of multiparametric magnetic resonance imaging for extracapsular extension, further tools are necessary to stratify men at risk for occult extracapsular extension that would otherwise only become apparent on final pathology. Magnetic resonance imaging/transrectal ultrasound fusion guided biopsy Gleason score can help identify which men with prostate cancer have extracapsular extension that may not be detectable by imaging.

Magnetic resonance imaging-directed biopsy improves the prediction of prostate cancer aggressiveness compared with a 12-core transrectal ultrasound-guided prostate biopsy

The Gleason grading system is a fundamental indicator of the aggressive nature of prostate cancer (PCa). Diffusion-weighted imaging (DWI) and magnetic resonance (MR) spectroscopy (MRS) are methods for the assessment of PCa aggressiveness. The present study was designed to prospectively investigate whether transrectal ultrasound (TRUS)-guided MR imaging (MRI)-directed biopsies (TRUS‑MR‑Dbs) improve the prediction of PCa aggressiveness in comparison with 12-core TRUS-guided biopsies (TRUS‑Gbs). A total of 518 patients underwent pre-biopsy multi-parametric MRI to identify the clinically suspicious PCa regions. TRUS‑MR‑Dbs were performed on patients with suspected PCa by MRI in addition to TRUS‑Gbs. Only patients who underwent radical prostatectomy (RP) were included in the comparative analysis. TRUS‑biopsy was directed to those areas within suspicious regions with a minimum apparent diffusion coefficient obtained by DWI or with a maximum (choline + creatine)/citrate ratio obtained by MRS. The highest Gleason grades (HGGs) and the Gleason scores (GSs) of specimens were identified. The biopsies and RP results were evaluated using a McNemar test or χ2 analyses using Fisher' exact tests. MRI results were positive in 254 (49.0%) of the 518 patients. TRUS‑MR‑Db detected 165/254 (65.0%) cancer cases and TRUS‑Gb detected 190/518 (36.7%) cancer cases. Forty patients underwent RP. The TRUS‑MR‑Dbs method demonstrated a higher concordance rate (CR) with RP (89.6%) than TRUS‑Gbs (72.9%, P=0.008) for the overall HGG. The CRs with RP for TRUS‑MR‑Dbs vs. those for TRUS‑Gbs were 100 vs. 85.7% (P=0.5), 87.5 vs. 68.8% (P=0.031) and 50 vs. 50% (P=1) for HGG3, HGG4 and HGG5, respectively. The HGG CRs with RP for DWI‑directed biopsies (DWI-Dbs) vs. MRS-directed biopsies (MRS-Dbs) were 77.1 vs. 50.0% (P=0.015) for the overall tumors, 80.0 vs. 40.0% (P=0.003) for peripheral zone tumors and 69.2 vs. 76.9% (P=1) for transition zone tumors. A total of 37 (77.1%) and 25 (52.1%; P=0.007) tumors were assigned accurate GS for TRUS‑MR‑Dbs and TRUS‑Gbs, respectively. The results revealed that TRUS‑MR‑Dbs improved the prediction of PCa aggressiveness and that DWI-Dbs had a superior performance when compared with MRS‑Dbs in the peripheral zone.

High Diagnostic Ability of Multiparametric Magnetic Resonance Imaging to Detect Anterior Prostate Cancer Missed by Transrectal 12-Core Biopsy

We clarified the diagnostic ability of multiparametric magnetic resonance imaging to reveal anterior cancer missed by transrectal 12-core prostate biopsy based on the results of 3-dimensional 26-core prostate biopsy, which is a combination of transrectal 12-core and transperineal 14-core biopsies. The study population consisted of 324 patients who prospectively underwent prebiopsy multiparametric magnetic resonance imaging and then 3-dimensional 26-core prostate biopsy at a single institution. We defined transrectal 12-core negative cancer as cancer detected by transperineal 14-core but not transrectal 12-core prostate biopsy. We focused on cancer in the anterior region. Any findings suspicious for malignancy in the region anterior to the urethra on multiparametric magnetic resonance imaging were defined as an anterior lesion on imaging. Significant cancer was defined as a biopsy Gleason score of 4 + 3 or greater, a greater than 20% positive core and/or a maximum cancer length of 5 mm or greater. Associations between an anterior lesion on imaging and transrectal 12-core negative cancer were investigated. The overall cancer detection rate on 3-dimensional 26-core prostate biopsy was 39% (128 of 324 cases), of which 28% (36 of 128) were transrectal 12-core negative cancers. An anterior lesion on prebiopsy multiparametric magnetic resonance imaging was identified in 20% of men overall (65 of 324). Of men with and without an anterior lesion on imaging 40% (26 of 65) and 3.8% (10 of 259), respectively, had transrectal 12-core negative cancer. Significant transrectal 12-core negative cancer was observed in 0.4% (1 of 259 men) without an anterior lesion on imaging. Prebiopsy multiparametric magnetic resonance imaging revealed an anterior lesion in 92% of cases (11 of 12) of significant transrectal 12-core negative cancer. Prebiopsy multiparametric magnetic resonance imaging has the potential to efficiently select men who could advantageously undergo anterior samplings, in addition to transrectal 12-core prostate biopsy.

Usefulness of Pre-biopsy Multiparametric Magnetic Resonance Imaging and Clinical Variables to Reduce Initial Prostate Biopsy in Men with Suspected Clinically Localized Prostate Cancer

We evaluated the usefulness of pre-biopsy multiparametric magnetic resonance imaging and clinical variables to decrease initial prostate biopsies. We prospectively evaluated 351 consecutive men with prostate specific antigen between 2.5 and 20 ng/ml, and/or digital rectal examination suspicious for clinically localized disease. All men underwent pre-biopsy multiparametric magnetic resonance imaging and initial 14 to 29-core biopsy, including anterior sampling. Three definitions of significant cancer were defined based on Gleason score and cancer volume (percent positive core and/or maximum cancer length). The overall cohort was divided into men at low risk-prostate specific antigen less than 10 ng/ml and normal digital rectal examination, and high risk-prostate specific antigen 10 ng/ml or greater and/or abnormal digital rectal examination. We evaluated the frequency of significant cancer according to magnetic resonance imaging and risk categories. Clinical variables as significant cancer predictors were analyzed using logistic regression. The sensitivity, specificity, and positive and negative predictive values of magnetic resonance imaging were calculated with or without clinical variables for significant cancer. The frequency of significant cancer in men with negative vs positive magnetic resonance imaging was 9% to 13% vs 43% to 50% in the low risk group and 47% to 51% vs 68% to 71% in the high risk group. In men at low risk with negative magnetic resonance imaging prostate volume was the only significant predictor of significant cancer. In the low risk group the negative predictive value for significant cancer of a combination of positive magnetic resonance imaging and lower prostate volume (less than 33 ml) was 93.7% to 97.5%. Pre-biopsy multiparametric magnetic resonance imaging along with prostate volume decreases the number of initial prostate biopsies by discriminating between significant cancer and other cancer in men with prostate specific antigen less than 10 ng/ml and normal digital rectal examination.

Magnetic Resonance Imaging/Ultrasound Fusion Guided Prostate Biopsy Improves Cancer Detection Following Transrectal Ultrasound Biopsy and Correlates With Multiparametric Magnetic Resonance Imaging

A novel platform was developed that fuses pre-biopsy magnetic resonance imaging with real-time transrectal ultrasound imaging to identify and biopsy lesions suspicious for prostate cancer. The cancer detection rates for the first 101 patients are reported. This prospective, single institution study was approved by the institutional review board. Patients underwent 3.0 T multiparametric magnetic resonance imaging with endorectal coil, which included T2-weighted, spectroscopic, dynamic contrast enhanced and diffusion weighted magnetic resonance imaging sequences. Lesions suspicious for cancer were graded according to the number of sequences suspicious for cancer as low (2 or less), moderate (3) and high (4) suspicion. Patients underwent standard 12-core transrectal ultrasound biopsy and magnetic resonance imaging/ultrasound fusion guided biopsy with electromagnetic tracking of magnetic resonance imaging lesions. Chi-square and within cluster resampling analyses were used to correlate suspicion on magnetic resonance imaging and the incidence of cancer detected on biopsy. Mean patient age was 63 years old. Median prostate specific antigen at biopsy was 5.8 ng/ml and 90.1% of patients had a negative digital rectal examination. Of patients with low, moderate and high suspicion on magnetic resonance imaging 27.9%, 66.7% and 89.5% were diagnosed with cancer, respectively (p <0.0001). Magnetic resonance imaging/ultrasound fusion guided biopsy detected more cancer per core than standard 12-core transrectal ultrasound biopsy for all levels of suspicion on magnetic resonance imaging. Prostate cancer localized on magnetic resonance imaging may be targeted using this novel magnetic resonance imaging/ultrasound fusion guided biopsy platform. Further research is needed to determine the role of this platform in cancer detection, active surveillance and focal therapy, and to determine which patients may benefit.

Combined Multiparametric MRI and Targeted Biopsies Improve Anterior Prostate Cancer Detection, Staging, and Grading

To assess the efficacy of magnetic resonance imaging (MRI) in detection of suspicious anterior prostate lesions, and its role in staging and grading of anterior prostate cancer (APC). Between January 2008 and August 2009, 243 patients had prostate cancer diagnosed at 12-cores posterior systematic biopsies and additional 2-cores transrectal ultrasound-guided, free-hand-targeted biopsy at any area suspicious for malignancy at prebiopsy multiparametric MRI. We conducted a retrospective study of 45 of 243 (19%) patients with an area suspicious for malignancy at MRI predominantly located in the anterior part of the gland, for which targeted biopsies were positive. Targeted vs systematic biopsy cancer detection rate and upgrading based on length of cancer in the most involved core and Gleason score were measured. Of the 45 patients, 46 separate APCs were identified at MRI with positive targeted biopsies. APC was not detected by systematic biopsies in 21 (46%) cases and detected in 25 (54%) cases. For these 25 cases, median cancer length of the most involved core in targeted compared with systematic biopsies was 8 mm vs 1 mm (P <.001), respectively. Significant Gleason score upgrading was observed in 11 of 25 (44%) cases. Correlation coefficient between the cancer length on targeted biopsies and the antero-posterior diameter of the area suspicious for malignancy on MRI was r(2) = .6 (P <.001). Separate posterior cancer was diagnosed in 26 patients. Targeted biopsies based on a prebiopsy MRI-detected lesion improved detection rate, volume, and grade of APC compared with currently used 12-cores systematic biopsies.

Characterizing Clinically Significant Prostate Cancer Using Template Prostate Mapping Biopsy

Definitions of prostate cancer risk are limited since accurate attribution of the cancer grade and burden is not possible due to the random and systematic errors associated with transrectal ultrasound guided biopsy. Transperineal prostate mapping biopsy may have a role in accurate risk stratification. We defined the transperineal prostate mapping biopsy characteristics of clinically significant disease. A 3-dimensional model of each gland and individual cancer was reconstructed using 107 radical whole mount specimens. We performed 500 transperineal prostate mapping simulations per case by varying needle targeting errors to calculate sensitivity, specificity, and negative and positive predictive value to detect lesions 0.2 ml or greater, or 0.5 ml or greater. Definitions of clinically significant cancer based on a combination of Gleason grade and cancer burden (cancer core length) were derived. Mean±SD patient age was 61±6.4 years (range 44 to 74) and mean prostate specific antigen was 9.7±5.9 ng/ml (range 0.8 to 36.2). We reconstructed 665 foci. The total cancer core length from all positive biopsies for a particular lesion that detected more than 95% of lesions 0.5 ml or greater and 0.2 ml or greater was 10 mm or greater and 6 mm or greater, respectively. The maximum cancer core length that detected more than 95% of lesions 0.5 ml or greater and 0.2 ml or greater was 6 mm or greater and 4 mm or greater, respectively. We combined these cancer burden thresholds with dominant and nondominant Gleason pattern 4 to derive 2 definitions of clinically significant disease. Transperineal prostate mapping may provide an effective method to risk stratify men with localized prostate cancer. The definitions that we present require prospective validation.