Timo Soeterik

169 General Discussion and Future Perspectives disease patients, preferably by a randomised controlled trial assigning patients to either AS or immediate active treatment. In addition to adherence to less stringent selection criteria for AS, our analysis revealed that AS follow-up in routine clinical care is also less strict compared to that protocolled in most AS cohort studies (Chapter 3). Overall, less than half (43%) of all patients received follow-up testing concordant with the PRIAS protocol. 3 Our study’s main finding was that in PRIAS-eligible patients, discordant monitoring was not associated which an increased risk of metastasis. However, our analysis also revealed that discordant monitoring in those not meeting the PRIAS criteria at baseline, did increase the risk of metastasis. These results contribute to our joint effort to reduce burden of patients with prostate cancer opting for AS, and specific recommendations can be extracted from the study. For instance, our study’s main findings suggest follow-up schedules in PRIAS- eligible patients may be loosened; whereas strict follow-up is recommended in patients not meeting one or more PRIAS inclusion criteria. A limitation of the study includes the lack of standard use of MRI during AS follow-up. At present, it is advised that MRI should be performed at least once at some point during AS follow-up. 4 Our study was performed before these recommendations were published, resulting in the relatively high percentage of patients on AS who were monitored without application of MRI (55%). 3 This could impact the generalisability of our outcomes to the contemporary state of practice. In addition, evaluation of the use of MRI and/or subsequent MRI target biopsy during follow-up were not included in the analysis. As we assume that MRI in this retrospective cohort was done in case of an indication (e.g. signs of tumour progression), application of MRI during follow-up in selected patients could impact the association between discordant follow-up and AS outcome, and could have masked the true impact of discordant follow-up. IMPACT OF MAGNETIC RESONANCE IMAGING ON PROSTATE CANCER RISK CLASSIFICATION Use of mpMRI T-stage, instead of DRE T-stage, would lead to migration of one-third of newly diagnosed patients to a higher prostate cancer risk group (Chapter 4). The stage migration is consequential to the higher detection rates of non-organ-confined disease of mpMRI, compared with DRE. The higher detection rates are countered by higher rates of false positive test results, especially in patients with low-risk disease. However, given the overall 9% higher cumulative rate of true positive and true negative detected non- organ-confined disease cases at diagnosis, mpMRI should be regarded as a superior to DRE as a staging and risk classification tool. Question remains if these results provide sufficient evidence for fully abandoning DRE for local tumour staging. The upstaging of one-third of patients could translate into unnecessary treatment intensification in patients low- and intermediate-risk cancer, especially in those with false-positive stage ≥T3a test results. Although DRE is 10