Research articleSub-differentiating equivocal PI-RADS-3 lesions in multiparametric magnetic resonance imaging of the prostate to improve cancer detection
Introduction
Multiparametric prostate MRI (mpMRI) has become established in the diagnostic pathway of men with prostate cancer [1], [2], [3] and is now increasingly used in the pre-biopsy setting to allow selection of men with significant cancer for biopsy, while avoiding biopsy and unnecessary treatment in men without an MRI lesion [4], [5].
The recently updated Prostate Imaging-Reporting and Data System (PI-RADS) guidelines are aimed at standardizing MRI acquisition and interpretation using a 5-point scoring system [6], [7]. However, when MRI is being used to guide the clinical decision making process either in the context of a previous negative biopsy, or in biopsy naïve patients, this 5-point scale has to be translated into a binary decision of whether to biopsy or not. A PI-RADS score of 1–2 is considered a “negative” MRI, and has a >90% negative predictive value (NPV) for significant disease [8], [9], thus biopsy can be reasonably avoided. Conversely, a PI-RADS 4–5 lesion is of high probability and targeted biopsy is warranted. An intermediate PI-RADS 3 lesion, however, straddles this decision making process, and biopsy in this case is under debate [10], [11], [12]. The overall detection of cancer in indeterminate lesions has been shown to vary from 6.5% to 60% for any cancer and 4.1% to 21% for significant cancer [10], [13], [14], [15], [16]. This needs to be considered in the context of a “miss rate” of around 10% for a PIRADS score of 1–2. Importantly, detection rates have been shown to be higher in the peripheral zone [14] and as high as 40% in the context of a second-biopsy population [15], suggesting some PI-RADS 3 lesions deserve biopsy, whereas others could be safely deferred. Informing management of such lesions is particularly relevant given the reported prevalence of indeterminate of 20.5–26.3% using earlier Likert-based systems [10], [16], [17], [18] is predicted to increase with a switch to using the PI-RADS-version 2 reporting system [19].
The aim of this study therefore was to evaluate if equivocal PI-RADS 3 lesions on mpMRI of the prostate can be further differentiated using pre-defined T2- and diffusion-weighted imaging (DWI) criteria, in order to aid in the biopsy decision process.
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Study population
This single-institution retrospective study was part of an evaluation of transperineal prostate biopsies with the need for informed consent for data analysis waived by the local ethics committee. From January 2013 to April 2016, 155 consecutive patients with a dominant (index) lesion considered to be equivocal on mpMRI (PI-RADS 3) underwent transperineal prostate biopsies at our tertiary center. 4 patients were excluded due to hip replacements, 8 patients were excluded as their scans were
Results
59% (85/143) of index lesions were called in the transition zone and 41% (58/143) in the peripheral zone. At transperineal biopsy, 43% (61/143) patients had a GS 6–10 prostate cancer in the target area, 21% (30/143) patients had a GS ≥ 3 + 4 cancer, and 6% (9/143) a GS ≥ 4 + 3 cancer, resulting in an overall positive predictive value of 0.43 for any cancer and 0.21 for significant GS 7–10 cancer. The clinical characteristics are shown in Table 2. The PPV for each objective imaging criterion for either
Discussion
Our study shows that re-evaluation of equivocal MRI lesions by an experienced uroradiologist, using only topographical, T2WI, and DWI and assessing set imaging criteria, improved diagnostic accuracy. Adding a subjective recommendation of whether or not to biopsy a lesion improved the cancer yield to 32% for GS 7–10 cancers and justified the “deserves biopsy” recommendation. Conversely the NPV of 0.92 for “avoid biopsy” lesions is equivalent to the NPV of a negative MRI (PI-RADS 1–2), which is
Conclusions
Identification of certain objective imaging criteria as well as a subjective biopsy recommendation from an experienced radiologist can help to increase the predictive value of equivocal prostate lesions and inform the decision making process of whether or not to biopsy.
Conflicts of interest
None.
Acknowledgements
The authors acknowledge research support from Cancer Research UK, National Institute of Health Research Cambridge Biomedical Research Centre, Cancer Research UK and the Engineering and Physical Sciences Research Council Imaging Centre in Cambridge and Manchester and the Cambridge Experimental Cancer Medicine Centre.
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2020, European Urology FocusCitation Excerpt :One study also used a Likert scoring system [10]. Multiparametric MRI was performed at 3 T in 18 studies [9,15,16,18–20,23,26,27,29–34,36,38,39], at 1.5 T in four studies [21,25,35,37], and at 3 or 1.5 T in six studies [3,10,17,22,24,28]. Multiparametric MRI sequences were T2W, DWI, and DCE in 22 studies [3,9,10,15–18,20,22,24–36,39]; four studies used only T2W and DWI sequences [19,35,37,38]; and one study also added MR spectroscopy [21] (Table 1).