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MP36-16 DEVELOPMENT AND EXTERNAL VALIDATION OF A NOVEL MODEL TO IDENTIFY PATIENTS WITH EQUIVOCAL LESION AT MULTIPARAMETRIC MRI WHO CAN AVOID PROSTATE BIOPSY

INTRODUCTION AND OBJECTIVES: The aim of this study is to assess the predictors of csPCa in the largest available series of men with PIRADS 3 at mpMRI and to develop and externally validate an individualized risk model that may safely spare prostate biopsies in patients with a low probability to have csPCa. METHODS: We identified 406 PIRADS 3 patients who underwent mpMRI of the prostate and subsequent targeted and concomitant systematic biopsy at two tertiary care referral Centres between 2013 and 2018. All patients had a negative DRE and they either were biopsy naive or received a previous prostate biopsy. The study outcome was csPCa, defined as Gleason≥3+4 at prostate biopsy. Multivariable logistic regression analysis (MVA) was performed to develop a predictive tool for the study outcome. Predictors included age at biopsy, PSA (ng/ml), prostate volume (ml) and previous biopsy (naive vs. negative vs. positive). The predictive accuracy (PA) was quantified using the AUC and the calibration plot method. Multivariable-derived coefficients were used to develop a novel risk-calculator. External validation of the model was performed into a population of 183 PI-RADS 3 men who underwent targeted and concomitant systematic biopsy at three tertiary care referral Centres between 2013 and 2018, using the regression coefficient and adjusting for the prevalence of the disease. RESULTS: Overall, 27.0% (110/406) and 10.3% (19/183) patients had csPCa in the development and validation cohort. At MVA, age at biopsy (OR:1.07), PSA (OR:1.08) and prostate volume (OR:0.97) were independent predictors of csPCa (all p⩽0.001).The multivariable model had a PA of 0.78 and the calibration plot was excellent. A low-risk group having <15% risk of harbouring csPCa was found based on the MVA derived risk calculator. Avoiding prostate biopsies in low-risk group would allow to spare 29% of all biopsies at the cost of missing 6% of csPCa. The sensitivity and negative predictive value associated with 15% cut-off were 93 and 94%, respectively. External validation of our risk-calculator showed a PA of 0.70. The application of our risk-calculator in the external validation cohort would have spared 66% of prostate biopsies at the cost of missing 8% of csPCa in the validation cohort. CONCLUSIONS: An individual risk model was developed and externally validated relying on the largest available series of patients with PI-RADS 3 lesion at mpMRI. Using a 15% csPCa risk cut-off, our model would allow for a considerable reduction of prostate biopsies at the cost of missing a small number of csPCa cases. Source of Funding: None