PI-RADS Upgrading Rules: Impact on Prostate Cancer Detection and Biopsy Avoidance of MRI-Directed Diagnostic Pathways.

Background: PI-RADS incorporate rules by which ancillary sequence findings upgrade a dominant score to a higher final category. Evidence on the upgrading rules' impact on diagnostic pathways remains scarce. Objective: To evaluate the clinical net benefit of the PI-RADS upgrading rules in MRI-directed diagnostic pathways. Methods: This study was a retrospective analysis of a prospectively maintained clinical registry. The study included patients without known prostate cancer who underwent prostate MRI followed by prostate biopsy from January 2016 to May 2020. Clinically significant prostate cancer (csPCa) was defined as International Society of Urological Pathology (ISUP) grade group ≥2. csPCa detection was compared between dominant (i.e., no upgrade rule applied) and upgraded lesions. Decision curve analysis was used to compare the net benefit, considering the tradeoff of csPCa detection and biopsy avoidance, of MRI-directed pathways in scenarios considering and disregarding PI-RADS upgrading rules. These included biopsy-all pathway, MRI-focused pathway (no biopsy for PI-RADS ≤2), and risk-based pathway (use of PSA density ≥0.15 to select patients with PI-RADS ≤3 for biopsy). Results: The sample comprised 716 patients (mean age, 64.9 years; 93 with a PI-RADS ≤2 examination, 623 with total of 780 PI-RADS ≥3 lesions). Frequencies of csPCa were not significantly different between dominant and upgraded PI-RADS 3 transition zone lesions (20% vs 19%), dominant and upgraded PI-RADS 4 transition zone lesions (33% vs 26%), and dominant and upgraded PI-RADS 4 peripheral zone lesions (58% vs 45%) (p>.05). In the biopsy-all, per-guideline MRI-focused, MRI-focused disregarding upgrading rules, per-guideline risk-based, and risk-based disregarding upgrading rules pathways, csPCa frequency was 53%, 52%, 51%, 52%, and 48%, and biopsy avoidance was 0%, 13%, 16%, 19%, and 25%, respectively. Disregarding upgrading rules yielded 5.5 and 1.9 biopsies avoided per missed csPca for MRI-focused and risk-based pathways, respectively. At probability thresholds for biopsy selection of 7.5-30%, net benefit was highest for the per-guideline risk-based pathway. Conclusion: Disregarding PI-RADS upgrading rules reduced net clinical benefit of the risk-based MRI-directed diagnostic pathway when considering tradeoffs between csPCa detection and biopsy avoidance. Clinical Impact: This study supports the application of PI-RADS upgrading rules to optimize biopsy selection, particularly in risk-based pathways.