LAUSR

104 Background: MRI/US fusion guided prostate biopsy (FBx) has been shown to detect clinically significant prostate cancer (csCaP) at higher rates and with fewer cores than standard prostate biopsy. However, the number of targeted cores needed to accurately characterize lesions identified on multiparametric MRI (mpMRI) is unknown. This study sought to determine factors that predict the number of cores needed to accurately characterize lesions during FBx of patients on active surveillance. Methods: A retrospective analysis of a prospectively maintained database of all patients undergoing FBx at an academic referral center between May 2014 and January 2018 was conducted. At least two FBx cores were taken from each lesion identified on mpMRI. Patient and lesion specific factors were analyzed to determine factors that predict the necessity to obtain additional cores to detect csCaP. GEE-based univariate logistic regression model with exchangeable correlation was used to estimate the effects of clinical characteristics including race, BMI, PSA, PSA density (PSAD), lesion location, and PI-RADS score on the proportion of positive and negative agreement. Predictability of a significant continuous predictor was quantified by AUC. The most significant patient-level predictor (PSAD) was further analyzed to determine thresholds at which multiple cores per lesion are needed to avoid missing csCaP. Results: An analysis of a total of 1141 FBx were performed during the study time interval. PSA (OR=1.57, 1.20-2.05, p<0.01) and PSAD (OR=1.43, 1.11-1.85, p<0.01) significantly predicted positive agreement of csCaP. AUC for positive and negative agreement was 57.4 and 61.0 for PSA and 56.4 and 72.3 for PSAD, respectively. Using these thresholds, only 56% lesions would need double core targeted biopsy. In other words, up to 44% of lesions would be accurately characterized with a single biopsy core of the targeted lesion. Conclusions: These data indicate that in patients with a PSAD less than 0.11 ng/ml2 or greater than 0.26 ng/ml2, lesions may be acceptably characterized with a single targeted biopsy core.