Performance of multiparametric MRI appears better when measured in patients who undergo radical prostatectomy

Nancy N Wang,1 Richard E Fan,1 John T Leppert,1,2 Pejman Ghanouni,3 Christian A Kunder,4 James D Brooks,1 Benjamin I Chung,1 Geoffrey A Sonn1,3 1Department of Urology, Stanford University School of Medicine, Stanford, CA, USA; 2Veterans Affairs, Palo Alto Health Care System, Palo Alto, CA, USA; 3Department of Radiology, Stanford University School of Medicine, Stanford, CA, USA; 4Department of Pathology, Stanford University School of Medicine, Stanford, CA, USA Abstract: Utilization of pre-biopsy multiparametric MRI (mpMRI) is increasing. To optimize the usefulness of mpMRI, physicians should accurately quote patients a numerical risk of cancer based on their MRI. The Prostate Imaging Reporting and Data System (PIRADS) standardizes interpretation of mpMRI; however, reported rates of clinically significant prostate cancer (CSC) stratified by PIRADS score vary widely. While some publications use radical prostatectomy (RP) specimens as gold standard, others use biopsy. We hypothesized that much of the variation in CSC stems from differences in cancer prevalence in RP cohorts (100% prevalence) vs biopsy cohorts. To quantify the impact of this selection bias on cancer yield according to PIRADS score, we analyzed data from 614 men with 854 lesions who underwent targeted biopsy from 2014 to 2018. Of these, 125 men underwent RP. We compared the PIRADS detection rates of CSC (Gleason ≥7) on targeted biopsy between the biopsy-only and RP cohorts. For all PIRADS scores, CSC yield was much greater in patients who underwent RP. For example, CSC was found in 30% of PIRADS 3 lesions in men who underwent RP vs 7.6% in men who underwent biopsy. Our results show that mpMRI performance appears to be better in men who undergo RP compared with those who only receive biopsy. Physicians should understand the effect of this selection bias and its magnitude when discussing mpMRI results with patients considering biopsy, and take great caution in quoting CSC yields from publications using RP as gold standard. Keywords: counseling, image-guided biopsy, magnetic resonance imaging, patient selection, prostatic neoplasm