Impact of 68Ga-PSMA PET/MRI on the Accuracy of MRI-Derived Grading Systems for Predicting Extraprostatic Extension in Prostate Cancer

<b>Objectives</b>: Accurate preoperative staging and prediction of extraprostatic extension (EPE) are critical for optimal surgical planning in prostate cancer (PCa). This study evaluated the diagnostic accuracy of ⁶⁸Ga-PSMA PET for EPE assessment, compared it with the standardized multiparametric MRI (mpMRI)-derived EPE-grading system, and examined whether integrating semi-quantitative PSMA PET parameters improves diagnostic performance using hybrid PET/MRI. <b>Methods</b>: This retrospective, single-center study included treatment-naïve, biopsy-proven PCa patients who underwent ⁶⁸Ga-PSMA-11 PET/MRI followed by radical prostatectomy. Diagnostic accuracy was assessed for clinical variables (PSA, ISUP grade), mpMRI features, mpMRI-derived EPE-grading system, visual PET findings, and semi-quantitative PET parameters (SUVmax, SUVmean, PSMA-tumor volume [PSMA-TV]). Optimal cut-offs were determined using the Youden index. Multivariate logistic regression and receiver operating characteristic (ROC) analyses were performed to compare the predictive value of clinical, mpMRI, or PET-derived variables, with histopathology as the reference standard. <b>Results</b>: Forty-five patients were included; EPE was histologically confirmed in 19 (42.2%). Predictors of EPE included capsular irregularity, neurovascular bundle asymmetry, curvilinear contact length ≥ 1.5 cm, seminal vesicle invasion, tumor size ≥ 14.25 mm, EPE grade ≥ 2, ISUP grade ≥ 3, overt EPE on PET, SUVmax ≥ 13.84, SUVmean ≥ 7.20, and PSMA-TV ≥ 1.40 cm³. The highest ROC performance (AUC = 0.890) was achieved by combining overt EPE on PET, SUVmax, and PSMA-TV. Incorporating PET parameters or tumor size into the EPE-grading system improved predictive accuracy. <b>Conclusions</b>: PSMA uptake in the primary tumor is an independent predictor of EPE. Integrating PSMA PET with mpMRI may provide additional information for preoperative EPE assessment.