A retrospective, single-center study by Borde et al. (2025) highlighted that discrepancies between prostate volumes measured by MRI and transrectal ultrasound (TRUS) can significantly reduce the effectiveness of fusion-targeted biopsy compared to systematic biopsy. Motivated by this finding, we aimed to evaluate the differences between MRI-defined and ultrasound-defined prostate volumes during elastic fusion biopsy based on our clinical experience.

This single-center retrospective cohort study (December 2022–December 2023) included male patients with PSA >4 ng/mL or abnormal DRE and suspicious MRI lesions (PI-RADS ≥3). All underwent software-assisted fusion biopsy, comparing MRI-derived and intraoperative ultrasound-derived prostate volumes and their impact on Gleason grading. Among 26 patients diagnosed via both targeted and systematic biopsy, LOESS regression analysis assessed the relationship between MRI–US volume differences and the Gleason-grade ratio.

LOESS regression analysis showed that as the discrepancy between MRI and ultrasound prostate volumes increased, the Gleason-grade ratio (fusion vs. systematic) decreased, indicating a higher likelihood of undergrading in fusion biopsy. Patients with minimal volume differences generally had Gleason-grade ratios of 1.0 or higher, suggesting comparable or slightly higher grading with fusion biopsy. However, when the volume difference exceeded approximately 5% or 2 mL, fusion biopsy more frequently yielded lower Gleason scores than systematic biopsy. These findings suggest that MRI–US volume mismatch may compromise fusion biopsy accuracy and increase the risk of undergrading.

When MRI and ultrasound-derived prostate volumes differ by more than 5% or 2 mL, fusion errors may lead to a shift in the targeted region, increasing the likelihood of under-sampling tumors.