Omitting biopsy in Prostate Imaging Reporting and Data System 3? The role of Stockholm3 and prostate-specific antigen density findings from a prospective Swiss non-referral cohort.

Introduction
Prostate Imaging Reporting and Data System (PI-RADS) 3 ("equivocal") prostate magnetic resonance imaging (MRI) lesions pose a diagnostic challenge, particularly in non-referral settings with variable MRI quality. We evaluated whether prostate-specific antigen density (PSAD) and the Stockholm3 blood test can aid biopsy decisions for men with PI-RADS 3 lesions in a prospective, non-referral Swiss cohort.
Methods
Retrospective analysis of a prospective registry at a non-referral urology practice in Switzerland. From 2023 to 2025, men with PSA >1.5 ng/mL or suspicious digital rectal examination underwent Stockholm3 testing, MRI, and MRI-fusion plus systematic prostate biopsy. Clinically significant prostate cancer (csPCa) was defined as the International Society of Urological Pathology (ISUP) grade ≥2. Diagnostic accuracy and decision curve analysis compared Stockholm3 (≥13%, ≥15%, and ≥18%) and PSAD thresholds (0.10, 0.15, and 0.20 ng/mL/cc) within the PI-RADS 3 subgroup.
Results
Overall, 50 of 174 (29%) men had PI-RADS 3 lesions, 59 of 174 (34%) were diagnosed with csPCa. Among PI-RADS 3 lesions, csPCa prevalence was 14%. Outcome distributions shifted toward higher ISUP grades with increasing PSAD thresholds when compared to the baseline (≥0.15 ng/mL/cc: 44% ISUP≥2; P = 0.009), whereas Stockholm3 cut-offs showed no significant change for csPCa. As continuous measures, PSAD demonstrated superior discrimination (area under the receiver operating characteristic curve: 0.751; 95% confidence interval: 0.46-0.95) than Stockholm3 (area under the receiver operating characteristic curve: 0.595; 95% confidence interval: 0.30-0.88), confirming higher overall diagnostic accuracy within the PI-RADS 3 subgroup. Decision curve analysis demonstrated higher net benefit for PSAD-based approaches.
Conclusion
In non-referral practice, Stockholm3 did not reliably exclude csPCa among men with PI-RADS 3 lesions. PSAD-based triage, particularly at ≥0.15 ng/mL/cc, showed superior diagnostic utility and may support safe biopsy deferral in selected cases. Prospective validation in broader non-referral settings is warranted.