Review article
Performance of multiparametric magnetic resonance imaging in the evaluation and management of clinically low-risk prostate cancer

https://doi.org/10.1016/j.urolonc.2013.04.002Get rights and content

Abstract

Objective

The purpose of this article is to review the multiparametric magnetic resonance imaging (mMRI) of the prostate and MR-guided prostate biopsy, and their role in the evaluation and management of men with low-risk prostate cancer.

Methods

We performed a literature review based on the MEDLINE database search for publications on the role of mMRI (a) in detection and localization of prostate cancer, prediction of tumor aggressiveness and progression and (b) in guiding targeted prostate biopsy.

Results

The mMRI, particularly diffusion-weighted imaging with T2-weighted imaging, is a useful tool for tumor localization in low-risk prostate cancer as it can detect lesions that are more likely missed on extended biopsy schemes and can identify clinically significant disease requiring definitive treatment. The MR-guided biopsy of the most suspicious lesions enables more accurate and safer approach to guide enrollment into the active surveillance program. However, the MR-guided biopsy is complex. The fusion of MRI data with transrectal ultrasound for the purpose of biopsy provides a more feasible technique with documented accurate sampling.

Conclusion

Although the mMRI is not routinely used for risk stratification and prognostic assessment in prostate cancer, it can provide valuable information to guide management of men with low-risk disease. Incorporation of mMRI into the workup and monitoring of patients with low-risk prostate cancer can help discriminate clinically significant disease from indolent disease. Targeted biopsy of MR-suspicious lesions enables accurate sampling of potentially aggressive tumors that may affect outcomes.

Introduction

As a consequence of widespread use of prostate-specific antigen (PSA) for prostate cancer screening, high-risk prostate cancers that are amenable to curative therapy are diagnosed earlier. However, at the same time, widespread screening is also associated with false-positive results and detection and overtreatment of low-risk disease. Active surveillance (AS) of prostate cancer is a viable option for the management of low-risk disease. This approach not only reduces the risk of overtreatment of indolent disease, but also appears to provide similar disease-free outcomes when compared with immediate treatment [1]. The most widely used criteria for categorization of low-risk disease are pathologic features described as (1) Gleason ≤ 6 without any Gleason pattern 4 or 5, (2) organ-confined disease, and (3) tumor volume<0.5 cm3 [2], [3].

Although Gleason 6 has been reported to be associated with disease progression after radical prostatectomy, reassessment of prostatectomy specimens revealed undergrading, understaging, and uncertain staging (intraprostatic incision), or grading (presence of tertiary pattern 4) in a setting of disease progression following radical prostatectomy. With precise histologic evaluation, the risk of disease progression after surgery in men with low-risk disease is very low (0.4%) [4].

There are wide variations in pathologic biopsy parameters used for inclusion into AS programs. However, the rate of unfavorable disease is still high and even with strictest criteria and use of 20 plus core biopsy protocol, 20% of patients are misclassified as having a low-risk disease [5].

Few nomograms have been reported to discriminate low-risk disease from clinically significant disease. The most predictive model was suggested by Chun et al. with 90% predictive accuracy of low-risk disease detection [6]. The earliest nomogram was developed by Kattan and colleagues [7]. Recently, they have incorporated imaging findings, from the magnetic resonance imaging and spectroscopy (MRI/MRSI) to the Kattan nomogram and have validated the new models. The area under the curve (AUC) increased from 0.558 to 0.741 in a base model and from 0.707 to 0.762 in another model incorporating percent of positive biopsy cores [8].

MRI has emerged as a promising tool for the evaluation of the prostate because with its high soft tissue contrast, it allows morphologic assessment of the gland, and with its capabilities to evaluate molecular and physiologic parameters of tissues, it aids in detection of metabolic, diffusion, and perfusion abnormalities associated with cancer.

Reclassification of disease in patients undergoing AS mainly occurs 1 to 2 years after the diagnosis, which is primarily owing to undersampling of the more aggressive tumor rather than progression of indolent tumor [9], [10]. These sampling errors result from the lack of access to the more aggressive lesions located anteriorly in the transition zone (TZ) or blind biopsy of lesions even with systematic extended biopsy schemes. Therefore, the introduction of MR-targeted biopsy allowed a more accurate sampling of the most suspicious lesions detected on imaging.

In this article, we review the multiparametric MRI (mMRI) of the prostate and MR-guided prostate biopsy, and their role in the evaluation and management of men with low-risk prostate cancer.

Section snippets

Morphologic MR imaging

The morphologic imaging with T2-weighted imaging (T2WI) gives a picture of the zonal anatomy of the prostate. The peripheral zone (PZ) tumors are typically detected as low signal intensity lesions on the high signal intensity background of normal tissue on T2WI. However, T2WI alone is neither sensitive (47.8%–88.2%) nor specific (44.3%–81%) for prostate cancer detection and should be interpreted in combination with other functional MR parameters [11]. For instance, there are some benign

Tumor localization in low-risk disease

Early studies showed that the addition of functional imaging parameters improves the sensitivity of tumor detection. However, those early studies mostly used low-strength field scanners with a limited specificity [30].

A combination of T2WI, DWI, and DCE-MRI was reported as the best protocol for imaging of unilateral low-risk PZ cancer with sensitivity and specificity of 85% and 83%, respectively. Although the combination of T2WI and DWI is the best imaging protocol for detection of TZ tumors in

Prediction of tumor laterality

Hemiablative focal therapy is a potential treatment method for patients with unilateral clinically significant disease (CSD). Matsuoka et al. assessed the performance of DWI and extended combined transperineal and transrectal ultrasound (TRUS)-guided biopsy to detect unilateral CSD or any indolent disease. They demonstrated that DWI, biopsy, and the combination of the 2 can effectively rule out the presence of any cancer (either indolent or CSD) in 22.1%, 27.8%, and 43.5%, respectively, and

Detection of anterior/TZ prostate cancer

The anterior prostate cancers (APC), comprising approximately 21% of all types of prostate cancer, are anatomically located in anteromedial and inferior portions of TZ or the anterior horns of PZ or both [36].

These tumors are not only nonpalpable with rectal examination but also hard to detect with TRUS biopsy [37]. Moreover, TZ-directed needle biopsy does not detect the dominant TZ lesion in approximately 80% of cases. Thus, screening needle biopsy from TZ is not a reliable method for

Prediction of prognostic outcome

Endorectal MRI has been shown to be useful for prediction of prognosis of intermediate- and high-risk diseases. It appears that radiologic distinction of T3 vs. T2 disease is predictive of a significantly worse biochemical outcome in patients with intermediate- and high-risk prostate cancers [50].

The predictive value of mMRI for prognostic outcome of low-risk patients eligible for AS has not been widely studied. Tumor inapparency at imaging is part of definition of stage T1 disease. Cabrera et

Tumor grading

In a study by Tamada et al. [57], ADC values in PZ tumors are in significant negative correlation with tumor Gleason score (r = 0.497). Similarly, Doo et al. [32] reported that the mean ADC value of tumors with Gleason 7 or higher (779.4×106 mm²/s) is significantly lower than that of low-grade tumors with Gleason 6 (874.6×106 mm2/s). Another study documented a significant negative correlation between the ADC values and cellular density (r = −0.50); cancer tissues with lower ADC values have higher

Targeted prostate biopsy

The accurate and adequate prostate sampling is crucial for determination of both patient eligibility for AS and disease monitoring. The importance of immediate repeat biopsy was evident in a study from Memorial Sloan-Kettering Cancer Center. In this study, repeat targeted biopsy in 3 months of initial biopsy session revealed upstaging and upgrading in 27% of patients eligible for AS. Authors recommended the immediate repeat biopsy for discrimination of best candidates of AS [54].

There is higher

Conclusion

The mMRI, particularly DWI with T2WI, is a useful tool for tumor localization in low-risk prostate cancer and can detect lesions that are more likely missed on extended biopsy schemes. Although the mMRI is not routinely being used for risk stratification and prediction of prognosis in prostate cancer, it may provide valuable information to predict outcome of men with low-risk disease in AS programs. Incorporation of mMRI into the workup and monitoring of patients with low-risk disease can help

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