#1378

Retrospective Review of the Diagnostic Performance of PSMA PET/CT versus mpMRI in the T staging of Clinically Significant Prostate Cancer

M. Rosario¹, R. Klein Nulend¹, J. Thomas², C. Chen², A. Atabaki², A. Dhar¹, L. Rahman², L. Kim¹, M. Patel¹

¹Westmead Hospital, Urology, Sydney, Australia
²Westmead Hospital, Nuclear Medicine, Sydney, Australia

Introduction:

Multiparametric MRI (mpMRI) is a well-established tool for pre-biopsy assessment in suspected prostate cancer. Prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT), while traditionally used for staging nodal and distant metastases, is emerging as a valuable modality in primary staging, including assessment of seminal vesicle invasion (SVI). However, comparative data between mpMRI and PSMA PET/CT in this context remain limited. This study assesses the diagnostic performance of mpMRI and PSMA PET/CT in predicting adverse pathological features in patients undergoing radical prostatectomy.

Material and methods:

A retrospective analysis was conducted on patients who underwent radical prostatectomy between 2016 and 2024 under urologists within the Western Sydney Local Health District. Imaging findings from pre-operative mpMRI and PSMA PET/CT were compared with final histopathology. A positive mpMRI was defined as presence of a PI-RADS 3–5 lesion. Tumour characteristics including ISUP grade, cribriform architecture, intraductal features, SVI, and extra-prostatic extension (EPE) were evaluated. SUVmax was analysed in correlation with these features using Kruskal-Wallis and Mann-Whitney U tests.

Results:

A total of 240 patients were included (mean age: 67 years). PI-RADS 5 lesions were seen in 63% of cases. Histopathology most commonly revealed ISUP grade group 2 (52%), with 74% showing multifocal acinar adenocarcinoma, 18% intraductal carcinoma, and 2% ductal histology. Cribriform architecture was present in 53%, with EPE in 52% and SVI in 11% of cases. SUVmax was significantly higher in patients with ISUP grade group 5 (median 16.9 [IQR 9.6–22.1]) compared to groups 2 and 3 (p < 0.001), as well as in patients with EPE (9.7 vs 6.0, p < 0.001), SVI (13.0 vs 6.5, p < 0.001), and intraductal carcinoma (10.0 vs 6.4, p = 0.008). Cribriform architecture was not associated with significantly elevated SUVmax. Diagnostic performance for predicting SVI was highest with PSMA PET/CT (sensitivity 62%, specificity 95%), compared to mpMRI alone (sensitivity 19%, specificity 97%). Combining both modalities resulted in a sensitivity of 53% and specificity of 91%. Negative predictive values were high across all modalities (>90%).