Man on active surveillance for prostate cancer (Gleason 3 + 3) diagnosed in 2010 4 cores of a TRUS standard 12-core biopsy (4 mm maximum cancer core length). The mpMRI scans show a left-sided peripheral zone lesion (arrows) characterized by low signal intensity on T2-weighted imaging, restricted diffusion in the ADC map and focal enhancement on dynamic contrast-enhanced sequences. The lesion did not show significant progression on mpMRI and this man is still on active surveillance
Man on active surveillance for prostate cancer (Gleason 3 + 3) diagnosed in 2003 on TRUS biopsy in up to 3 mm of 3/22 cores. The mpMRI scans show a left-sided peripheral zone lesion between the apex and mid-gland (arrows) abutting the prostatic capsule characterized by low signal intensity on T2-weighted imaging, restricted diffusion in the ADC map and focal enhancement on dynamic contrast-enhanced sequences. The lesion did not show significant progression on mpMRI until 2014, when the T2-weighted images suggest a slow progression of the lesion (likely T3a disease). Subsequent biopsy demonstrated overall Gleason score 3 + 4, with maximal Gleason 4 + 3 in five out of nine cores. This man underwent radical prostatectomy confirming Gleason 4 + 3 and T3a disease at left posterior surgical margin
Currently, different groups are using different parameters. Morgan et al.  defined progression as cases that progressed to radical treatment, rather than according to radiological or histopathological criteria alone. The difficulty here is that it can lead to a circular argument, if the clinician is aware of the mpMRI changes and moved to offer radical treatment because of the change on mpMRI.
The National Institute of Health (NIH) group used change in size of a lesion, change in appearance of a lesion and appearance of a new lesion to define radiological and found that when all three characteristics were present, then the rate of pathological progression from International Society of Urological Pathologist (ISUP) grades 1–2 or 2–3  was 100%, compared to 33.3% when only one characteristic was seen .
A panel of experts, convened by the European School of Oncology, has recently published the Prostate Cancer Radiological Estimation of Change in Sequential Evaluation (PRECISE) guidelines , in order to facilitate robust data collection of mpMRI in active surveillance. Using these guidelines in reporting mpMRI at baseline and follow-up in men on active surveillance will allow assessment of the natural history of mpMRI findings in men on active surveillance. The PRECISE recommendations include a score for the likelihood of change between a baseline and follow-up mpMRI. If widely used, the data derived from the application of these guidelines would facilitate the determination of thresholds that identify radiological significant disease and important radiological changes on mpMRI .
Nassiri et al.  analysed 259 men on active surveillance (196 with Gleason score 3 + 3 and 63 with Gleason score 3 + 4) who were diagnosed by MRI/US fusion-guided biopsy and who underwent subsequent fusion biopsy for as long as 4 years of active surveillance. The primary endpoint of the study was to determine the rate of upgrading to Gleason score ≥ 4 + 3 using targeted biopsy. The authors concluded that 63% of men with Gleason score 3 + 4 had upgraded by the third year of active surveillance, compared with 18% of men with Gleason score 3 + 3 at entry (p < 0.01). Interestingly, 97% of all upgrades (32/33) occurred within an mpMRI-visible lesion (n = 21) or a tracked site (n = 11). This suggests that the use of software-assisted biopsy, especially when tracking an mpMRI-visible lesion, could be of great help in the detection of potentially aggressive cancer during active surveillance.
Cost Implications of MRI to Inform Active Surveillance
The cost of mpMRI on active surveillance is often a factor in its use in a routine setting. Although the cost in some health care systems is high, it can be offset against the cost savings generated by delaying or avoiding surgery or other treatments. Gordon and colleagues  have evaluated the cost-effectiveness of mpMRI to diagnose prostate cancer and direct all low-risk patients to active surveillance. They developed a cohort model in three different scenarios (i.e. (i) no mpMRI but only active surveillance, (ii) mpMRI and active surveillance in a biopsy-naïve population and (iii) mpMRI and increased active surveillance uptake) and concluded that mpMRI and active surveillance in men with low-risk prostate cancer are strongly cost-effective (likelihood of 86.9%). For every 1000 men suspected of prostate cancer, using mpMRI could avoid 340 biopsies, detect an additional 20 significant cancers and detect 10 fewer insignificant cancers. However, this only addresses the use of a single mpMRI scan prior to first biopsy and not the use of follow-up mpMRI whilst on active surveillance. This would require an additional evaluation, in light of whether other tests (e.g. routine rebiopsy) could be omitted .
There is good evidence to support the use of mpMRI in men with an initial biopsy suitable for active surveillance, and to target any lesions seen on mpMRI, often in conjunction with a confirmatory systematic biopsy.
MpMRI may offer an opportunity to follow men on active surveillance without the need of performing further biopsies, in the absence of signs of progression. Although mpMRI is of interest for the monitoring of men on active surveillance, robust data from prospective studies are needed before widespread adoption of mpMRI can replace repeat biopsies.
Wilt TJ, Brawer MK, Barry MJ, Jones KM, Kwon Y, Gingrich JR, et al. The Prostate Cancer Intervention Versus Observation Trial:VA/NCI/AHRQ Cooperative Studies Program #407 (PIVOT): design and baseline results of a randomized controlled trial comparing radical prostatectomy to watchful waiting for men with clinically localized prostate cancer. Contemp Clin Trials. 2009;30:81–7.CrossrefPubMed