Low heterogeneity of tumor grades in multiple MRI-targeted prostate biopsies argues for the aggregate method of grading

Prostate cancer diagnosis primarily relies on histological confirmation via needle core biopsy, with systematic 12-core biopsies (SB) being commonly used. Multiparametric magnetic resonance imaging (mpMRI) and MRI-targeted biopsies have shown enhanced detection of clinically significant prostate cancer. This study compares two tumor grading methods-aggregate and individual grading-used in MRI-targeted biopsies to assess their correlation with the final ISUP Grade Group (GG) of the RPE. A cohort of 108 patients with ≥ 2 positive cores in at least one MRI-targeted biopsy, totaling 179 positive lesions, was analyzed. Systematic and MRI-targeted biopsies were correlated with RPE specimens. The mean highest ISUP GG for systematic biopsies was 2.77 (SD ± 1.29), compared to 2.62 (SD ± 1.13) for targeted biopsies using the aggregate method. Comparing the highest ISUP GG in systematic as well as targeted biopsies with the final ISUP GG of the RPE, exact correlation between GG was found in 70.1% (aggregate) and 66.4% (individual) for targeted biopsies and 58.1% for systematic biopsies. The results of the individual method showed slightly better correlation with the final ISUP GG from the RPE specimen in only 0.93%, while in 2.8% of cases, it resulted in inferior correlation compared to the aggregate method. Our findings suggest that the aggregate grading method of targeted biopsies is preferable due to its comparable predictive accuracy, lower workload, and alignment with existing clinical guidelines. This supports the ISUP's recommendation to use the aggregate method for MRI-targeted biopsies in clinical practice. Further research is needed to standardize reporting protocols for MRI-targeted biopsies and refine their integration into prostate cancer risk stratification models.