Objective
To investigate the utility of multiparametric magnetic resonance imaging (mpMRI) in the reassessment and monitoring of patients on active surveillance (AS) for Grade Group (GG) 1 prostate cancer (PCa).
Patients and Methods
We identified, from our prospectively maintained IRB‐approved database, 181 consecutive men enrolled on AS for GG 1 PCa who underwent at least one surveillance mpMRI followed by MRI/prostate biopsy (PBx). A subset analysis was performed among 68 patients who underwent serial (at least two) mpMRI/PBx during AS. Pathological progression (PP) was defined as upgrade to GG ≥ 2 on follow up biopsy. Statistically significant if p<0.05.
Results
Baseline MRI was performed in 34 (19%) patients. In a median follow up of 2.2 years for the overall cohort, the PP was 12% (6/49) for PIRADS 1‐2 and 37% (48/129) for PIRADS≥ 3. The 2‐year PP‐free survival was 84%. Surveillance PSA density (p<0.001) and surveillance PIRADS ≥ 3 (p=0.002) were independent predictors for PP on reassessment MRI/PBx. In serial MRI cohort, the 2‐year PP‐free survival was 95% for no MRI‐progression vs 85% for MRI‐progression group (p=0.02). MRI progression was significantly higher in PP (62%) than in no‐PP (31%) group (p=0.04). If serial MRI is used for PCa surveillance and biopsy is triggered based only on MRI progression, 63% of PBx might be postponed by the cost of missing 12% of GG≥2 PCa in those with stable MRI. Conversely, this strategy would miss 38% of those with upgrading to GG≥2 PCa on biopsy. Stable serial mpMRI correlates with no reclassification to GG ≥ 3 PCa during AS.
Conclusion
PIRADS ≥ 3 on surveillance mpMRI is associated with increased risk of PCa reclassification. Surveillance biopsy based only on MRI progression may avoid large number of biopsies with the cost of missing many PCa reclassification.
MP-MRI of the prostate in combination with targeted biopsies of visualized lesions is now a standard approach when active surveillance is considered for supposed low-risk prostate cancer.(1) It provides more adequate sampling of known malignant lesions and aids in detecting lesions missed by systematic biopsy alone. The stage shift resulting from this strategy also necessitates to adapt our classic risk categories and indication for active surveillance to the imaging-based diagnosis-era.(2)
The role of MRI to follow-up patients during active surveillance is evolving. The concept of MRI-based surveillance is without doubt very appealing. Standard repeat biopsies are incorporated in most of the existing active surveillance protocols, but are certainly the least attractive tool for follow-up, for both patient and urologist. By only performing biopsy in patients with progression on imaging, many unnecessary biopsies might be avoided and the yield of the procedure increased.
Fujihara et al provide additional evidence in this setting.(3) The authors found that although MRI findings are associated with reclassification rates, biopsying only those patients with progression would miss many of the cases that would have been found with standard biopsy for all men. The findings are in line with other reports such as by Hsiang et al and Chesnut et al.(4,5) May Biopsies still provide a more robust and standardized interpretation of true tumor status than subjective MRI?
MRI definitely has the potential to improve active surveillance follow-up. In light of screening for prostate cancer and the reduction of overtreatment, it is also essential to increase the acceptance of active surveillance and decrease the burden of this strategy. We need to remember that patients suitable for active surveillance have a very favorable outcome, whatever treatment is chosen. As said, in the MRI-targeted-biopsy-era, not all GG2 (Gleason 3+4) need treatment, so triggers for therapy need to be adapted accordingly. Also, the harm of delaying the detection of upgrading until the moment it is visualized on MRI may not have an unfavorable impact on long-term outcomes. Furthermore, novel scoring systems (PRECISE) for this purpose will improve interpretation.(6) Despite conflicting results so far, the incorporation of MRI findings in a risk-based active surveillance follow-up approach has a great potential.
1. Mottet et al. European Association of Urology guidelines for prostate cancer 2020
2. Ploussard et al. Decreased accuracy of the prostate cancer EAU risk group classification in the era of imaging-guided diagnostic pathway: proposal for a new classification based on MRI-targeted biopsies and early oncologic outcomes after surgery. World J Urol. 2020 Oct;38(10):2493-2500
3. Fujihara et al. Multiparametric Magnetic Resonance Imaging Facilitates Reclassification During Active Surveillance for Prostate Cancer. BJU Int. 2020 Oct 11
4. Hsiang et al. Outcomes of Serial Multiparametric Magnetic Resonance Imaging and Subsequent Biopsy in Men with Low-risk Prostate Cancer Managed with Active Surveillance. Eur Urol Focus. 2019 May 27:S2405-4569(19)30148-8
5. Chesnut et al. Role of Changes in Magnetic Resonance Imaging or Clinical Stage in Evaluation of Disease Progression for Men with Prostate Cancer on Active Surveillance. Eur Urol. 2020 Apr;77(4):501-507
6. Giganti et al. Natural history of prostate cancer on active surveillance: stratification by MRI using the PRECISE recommendations in a UK cohort.Eur Radiol. 2020 Sep 30