Does Size Matter? Lesion Size As An Indicator Of Number Of Cores Needed To Detect Clinically Significant Prostate Cancer

283 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. Size plays an important role in assigning a suspicion level (PI-RADS) to lesions identified on MRI. However, tumor characteristics may pose challenges to accurately characterizing the lesion despite the size. This study sought to determine if there are size cutoffs at which a lesion may be accurately characterized as clinically significant cancer with a single biopsy core. 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. GEE-based univariate logistic regression model with exchangeable correlation was used determine if size was a significant predictor of positive and negative agreement. Predictability of size as a significant continuous predictor was quantified by AUC. Size thresholds at which multiple cores per lesion are needed to avoid missing > 2% of csCaP were calculated, allowing for a 25% discordance rate. Results: An analysis of a total of 1141 FBx of 2200 lesions was performed during the study time interval. Size was a significant predictor of both positive (OR = 2.43, 1.83-3.23, p < 0.01) and negative (OR = 0.58, 0.44-0.76, p < 0.01) agreement of csCaP. AUC% for positive and negative agreement was 65.8 and 57.6, respectively. Size thresholds of 0.65 and 1.70 cm limited CS cancers missed by skipping a second targeted biopsy core to 2% while allowing for a 25% discordance. Conclusions: These data indicate that clinically significant prostate cancer in lesions less than 0.65 cm and greater than 1.70 cm may be characterized with a single targeted biopsy core, sparing 33.5% of lesions (21% patients) a double core targeted biopsy.