Timo Soeterik

121 Development of a novel EPE nomogram BACKGROUND A challenging aspect of performing the radical prostatectomy (RP) for prostate cancer includes balancing the risk of positive margins versus optimisation of quality of life by maximising the probability of retaining the patient’s erectile function and urinary continence. In 1982, the first purposeful nerve sparing radical prostatectomy was performed, resulting in a normal postoperative sexual function and retained quality of life of the patient. 1 Following the introduction of this technique, its therapeutic effect has been evaluated in several other studies. A recent meta-analysis showed nerve sparing to be associated with a lower risk of postoperative incontinence (relative risk [RR] 0.75, 95% confidence interval [CI] 0.65 - 0.85) and erectile dysfunction (RR 0.77, 95% CI 0.70 – 0.85). 2 Preoperative assessment of extraprostatic extension (EPE) is a long-established strategy to guide patient selection for nerve sparing. If there is a high risk of EPE, nerve sparing should be discouraged due to the increased risk of positive surgical margins. 3 EPE risk prediction is often done using nomograms such as the Partin tables and the MSKCC nomogram. 4,5 However, these models do not provide information on the laterality of EPE. Since EPE is mostly one-sided (85%), localisation is essential as unilateral nerve sparing surgery remains possible in the majority of patients. 6 Nomograms predicting side-specific EPE have also been developed. However, these models lack the inclusion of multiparametric magnetic resonance imaging (mpMRI) information. 6-8 Adoption of mpMRI to guide clinical decision-making in prostate cancer has drastically increased recent years. 9 MpMRI alone has limited ability to guide patient selection for nerve sparing, due to a low per-patient sensitivity for the detection of EPE of 57%. 10 However, its predictive potential when combined with other clinical parameters remains poorly understood. Previous studies have shown that combining mpMRI information with traditional preoperative clinical parameters including biopsy information and serum prostate-specific antigen, can improve the prediction of adverse surgical pathology including EPE. 11,12 The number of available nomograms including a combination of both mpMRI and clinical parameters for the prediction of side-specific EPE, however, is scarce. The need for further exploration of the additional value of using mpMRI information for the prediction of side-specific EPE is emphasised by the results of a recent external validation study; showing that mpMRI-naive nomograms are inaccurate when applied in external populations. 13 Therefore, we aim to develop a nomogram that enables accurate prediction of side- specific EPE, applicable in current state of clinical practice, including readily available clinical and MRI input parameters. Generalisability of the tool will be assessed by performing external validation using two separate hospital populations. 7