Marieke van Son

10 CHAPTER 1 prove the diagnostic yield of clinically significant cancer, while reducing over-diagnosis of low-risk disease as compared to systematic biopsies(13-15). The clinical utility of systematic biopsies in such an “MRI pathway” has even been questioned in more recent work, showing that the detection of clinically significant cancer in exclusively non-tar- geted biopsies can be as low as 2%(16). In the pre-treatment setting, mp-MRI also provides a predictive ability of extracapsular extension, aiding urologists in their preop- erative planning and radiation oncologists in selecting their treatment regimen(17-19). To improve inter-reader reproducibility, much effort has been put into creating clear guidelines to ensure standardized mp-MRI acquisition and interpretation(20). Figure 3 - Four main prostate cancer tumor stages. T1 is divided into T1a (cancer unexpectedly found in <5% of removed tissue), T1b (cancer unexpectedly found in ≥5% of removed tissue) and T1c (cancer found by biopsy). T2 is divided into T2a (≤half of one side of the gland), T2b (>half of one side of the gland) and T2c (both sides). T3 is divided into T3a (broken through the capsule) and T3b (spread into the vesicles). Image adapted from: Cancer Research UK (www.cancerresearchuk.org ). After manual and radiological examination, a definitive prostate cancer diagnosis re- quires histopathological verification of adenocarcinoma. The International Society of Urological Pathology (ISUP) constructed the Gleason score system, which consists of a score for the most extensive pattern plus the second most common pattern and a sum score. Nowadays, Gleason scores are reported by the classification of five grade groups, i.e. sum score ≤6 (group 1), 3+4=7 (group 2), 4+3=7 (group 3), sum score 8 (group 4) and sum score 9-10 (group 5)(21). There are several definitions of what is considered “clinically significant prostate cancer” (i.e. cancer that requires treatment), ranging from any ISUP grade 2 or 3 to ISUP grade 3 / ≥6mm of ISUP grade 1 or ISUP grade 2 / ≥4mm of ISUP grade 1(22). A combination of these features (clinical T-stage, ISUP grade group, serum PSA-level) allows for stratification of patients into prognostic groups based on risk of recurrence after treatment. Low-, intermediate- and high-risk groups have been identified by sev- eral guideline committees(23-26), all with minor differences regarding the definition of intermediate- and high-risk disease (Table 1). To further aid individualized treatment