Evaluating extraprostatic extension of prostate cancer: pragmatic integration of MRI and PSMA-PET/CT.

[PURPOSE] To explore pragmatic approaches integrating MRI and PSMA-PET/CT for evaluating extraprostatic extension (EPE) of prostate cancer (PCa).

[METHODS] Consecutive patients with newly-diagnosed PCa that underwent multiparametric MRI and PSMA-PET/CT, followed by radical prostatectomy in 2021-2024 were included. Imaging parameters assessed on both modalities were: size, length of capsular contact (LCC), Likert scales (MRI EPE grade/PSMA Likert scale), PI-RADS/PRIMARY scores, and SUV. Three pragmatic integrated approaches were tested: (1) Integration of Likert scales (positive if either or both MRI and PSMA-PET/CT were positive); (2) P score (framework combining PI-RADS + PRIMARY); and (3) combining MRI morphological information with PSMA-PET/CT functional information (upgrading suspicion of lesions with LCC below cutoff if SUV>12). Diagnostic performance was tested with receiver operating characteristic (ROC) curves and compared using DeLong and McNemar tests.

[RESULTS] 67 men (median age, 66 years) with EPE in 76.1% (51/67) were included. Area under ROC curves (AUC) were 0.61-0.82; MRI-based LCC yielded the highest AUC 0.82 (0.71-0.92) with cutoff of ≥ 1.7 cm. Integrated Likert scale (MRI EPE grade/PSMA Likert scale) showed sensitivity of 80.4% (41/51) and specificity of 31.3% (5/16). P score (PI-RADS/PRIMARY) demonstrated sensitivity of 31.3% (16/51) and specificity of 87.5% (14/16). Combining morphological MRI information with functional PSMA-PET/CT yielded sensitivity and specificity of 80.4% (41/51) and 81.2% (13/16), respectively, which demonstrated significantly higher sensitivity but non-significantly different specificity compared with MRI-based LCC alone (66.7% [34/51, p = 0.02] and 87.5% [14/16, p > 0.99]). This approach upgraded suspicion in 8 patients with LCC < 1.7 cm due to SUV>12 among which 87.5% (7/8) were corrected upgraded and had pathological EPE.

[CONCLUSION] Several pragmatic approaches were explored for integrating MRI and PSMA-PET/CT to assess EPE in PCa. Combining morphological information from MRI and PSMA expression on PET/CT demonstrated good diagnostic performance and may be a simple pragmatic integrated method that can be used.