Accurate detection and grading of prostate cancer remain critical challenges in urologic oncology, with multiparametric MRI (MRIp) playing a central role in pre-biopsy evaluation. However, emerging evidence suggests that prostate volume significantly impacts MRI sensitivity and ISUP grading accuracy, particularly in larger glands where lesion conspicuity may be reduced [1]. Tumor underestimation in MRIp can lead to misclassification and suboptimal management decisions[2]. As PSMA PET imaging gains prominence, its utility in overcoming volumetric limitations warrants exploration. This study investigates how prostate size influences MRI performance using a Biobot-guided biopsy and radical prostatectomy dataset, aiming to optimize diagnostic pathways.

A prospective analysis was conducted using the Biobot prostate cancer database, encompassing 56 patients who underwent multiparametric MRI (mpMRI), PSMA PET, and radical prostatectomy (RP) between October 2022 and February 2025. Patients were stratified by prostate volume into three groups: ≤20 cc, 21–29 cc, and ≥30 cc based on MRI measurements. mpMRI-assigned ISUP grade groups (1–2 vs. 3–5) were compared to final RP histopathology to evaluate diagnostic accuracy. Accuracy was categorized as complete, underestimated, or overestimated. Subgroup analysis examined the correlation between prostate volume and MRI grading performance, aiming to identify patterns of diagnostic discrepancy across gland sizes.

In this cohort of 56 patients, MRI accuracy in predicting ISUP grade varied by prostate volume. In prostates ≤20 cc, MRI correctly identified ISUP grade in 71% of ISUP 1–2 and 82% of ISUP 3–5 cases. For volumes 21–29 cc, accuracy was 68% and 77%, respectively. In prostates ≥30 cc, accuracy declined to 60% for ISUP 1–2 and 70% for ISUP 3–5. Underestimation occurred more frequently in larger prostates. This difference in accuracy across volume groups was statistically significant (p = 0.026), suggesting that increasing prostate size negatively affects MRI performance in grading prostate cancer severity.

MRI accuracy in ISUP grading declines with increasing prostate volume, particularly due to underestimation in larger glands. These findings highlight the importance of considering prostate size when interpreting MRI results and support the use of adjunct imaging or biopsy strategies in larger prostates.