Prostate cancer risk stratification with magnetic resonance imaging

Abstract

In recent years, multiparametric magnetic resonance imaging (mpMRI) has shown promise for prostate cancer (PCa) risk stratification. mpMRI, often followed by targeted biopsy, can be used to confirm low-grade disease before enrollment in active surveillance. In patients with intermediate or high-risk PCa, mpMRI can be used to inform surgical management. mpMRI has sensitivity of 44% to 87% for detection of clinically significant PCa and negative predictive value of 63% to 98% for exclusion of significant disease. In addition to tumor identification, mpMRI has also been shown to contribute significant incremental value to currently used clinical nomograms for predicting extraprostatic extension. In combination with conventional clinical criteria, accuracy of mpMRI for prediction of extraprostatic extension ranges from 92% to 94%, significantly higher than that achieved with clinical criteria alone. Supplemental sequences, such as diffusion-weighted imaging and dynamic contrast-enhanced imaging, allow quantitative evaluation of cancer-suspicious regions. Apparent diffusion coefficient appears to be an independent predictor of PCa aggressiveness. Addition of apparent diffusion coefficient to Epstein criteria may improve sensitivity for detection of significant PCa by as much as 16%. Limitations of mpMRI include variability in reporting, underestimation of PCa volume and failure to detect clinically significant disease in a small but significant number of cases.

Keywords: MRI; Prostate cancer; Risk stratification.

Fig. 1

Likelihood of significant prostate cancer detection by MRI suspicion. Axial T2-weighted prostate images demonstrating peripheral zone lesions (arrows) of increasing suspicion. Examples are of a PI-RADS 3 target (left), a PI-RADS 4 target (center), and a PI-RADS 5 target (right). Percentages shown with asterisk represent likelihood of targeted biopsy revealing a cancer of Gleason Score 7 or greater, based on UCLA data (n = 1,200) (78). ^*Modified and reprinted with permission from European Urology 69(1); Weinreb et al. [19]. Copyright 2016, with permission from Elsevier. (Color version of figure is available online.)

Fig. 2

Prostate cancer detection rates for 3 different scoring systems, stratified by level of suspicion on MRI. A progressive increase in prostate cancer detection with increasing suspicion score is consistently shown for each of the 3 systems. (Data shown are for detection of all PCa, but a qualitatively similar pattern is also apparent for clinically significant disease). (Color version of figure is available online.)

Fig. 3

A 64-year-old man referred for possible enrollment into active surveillance, after conventional biopsy revealed Gleason 3 + 3 in 10% of 1 core. Top row—T2-weighted images, (A) (axial) and (B) (coronal). There is a large tumor in the left peripheral zone base (arrows), with findings suggestive of extracapsular extension (ECE) and involvement of the left seminal vesicle (SV). Bottom row—diffusion-weighted images, (C) (apparent diffusion coefficient map) and (D) (high b-value). There is markedly restricted diffusion within the tumor. Final pathology demonstrated Gleason 4 + 4 at the left base with ECE and SV invasion.