Interreader Variability in MRI-Guided Prostate Biopsy: Impact on ProScreen Trial

Overview

This study evaluated interobserver variability among six uropathologists interpreting MRI-targeted prostate biopsies in 85 men. Consensus on ISUP Grade Group was reached in 65.9% of cases, with complete agreement in 21.2%, highlighting variability that may influence clinical decisions in the ProScreen prostate cancer screening trial.

Background

Population-based prostate cancer screening using PSA and systematic biopsies reduces mortality but leads to overdiagnosis of clinically insignificant prostate cancer (cisPCa). Multiparametric MRI (mpMRI) with targeted biopsies improves detection of clinically significant prostate cancer (csPCa) and reduces cisPCa diagnosis. The ProScreen trial uses mpMRI-targeted biopsies to minimize overdiagnosis while aiming to reduce prostate cancer mortality. Accurate pathological grading of MRI-targeted biopsies is critical for appropriate treatment selection, yet interobserver agreement among pathologists in this context has not been previously studied.

Data Highlights

Key Findings

• Complete agreement on ISUP Grade Group among all six pathologists occurred in 21.2% (18/85) of cases; 72.2% of these were benign.
• Consensus defined as ≥2/3 agreement was reached in 65.9% (56/85) of cases.
• In 13 cases, consensus grading differed from the original diagnostic grade, but 92.3% of these disagreements were within ±1 Grade Group.
• No consensus was reached in 34.1% (29/85) of cases, with the main disagreement source being the estimated proportion of Gleason pattern 4 or 5.
• Pathologists had varying clinical experience (3 to 50 years), and no formal common training was provided before assessments.

Clinical Implications

Interreader variability in grading MRI-targeted prostate biopsies may impact clinical decision-making in prostate cancer screening trials like ProScreen. Establishing standardized training and consensus guidelines for pathologists interpreting targeted biopsies could improve diagnostic consistency and optimize treatment selection. Awareness of variability is important when using mpMRI-targeted biopsy results to guide patient management.

Conclusion

This validation study demonstrates moderate interobserver agreement among uropathologists in grading MRI-targeted prostate biopsies, underscoring the need for standardized pathology protocols to support accurate diagnosis and effective prostate cancer screening.

References

1. Eklund et al. 2020 -- MRI-Only vs Systematic Biopsies in Prostate Cancer Detection
2. ISUP Consensus Conference 2019 -- Reporting of Systematic vs Targeted Prostate Biopsies
3. ProScreen Trial Protocol 2018 -- Population-Based Prostate Cancer Screening