Localization of PSMA-avid lesions on PSMA PET-CT on prostate MRI in patients with PI-RADS 3

To localize PSMA-avid lesions identified by PSMA PET-CT on separately performed prostate MRI and evaluate imaging findings on fused PET-CT/MRI.

Patients without prior history of clinically significant prostate cancer (csPCa: Gleason score [GS] 3 + 4 or higher) who had (1) PI-RADS 3 on prostate MRI between 2021 and 2023, (2) MRI/US fusion targeted biopsy for PI-RADS 3 lesion(s) and systemic biopsy, and (3) subsequent PSMA PET-CT were identified. PSMA PET-CT images were fused onto prostate MRI. PI-RADS 3 lesions were categorized by PRIMARY score. Discordant PSMA-avid lesions with PRIMARY scores 2-5 outside of PI-RADS 3 lesions were identified. Fisher's exact test was used to compare the proportion of csPCa on targeted biopsy between PSMA-positive (PRIMARY score 3 or more) and PSMA-negative (PRIMARY score 1 or 2) PI-RADS 3 lesions. P < 0.05 was considered statistically significant.

30 patients (mean age 67 years) with 38 PI-RADS 3 lesions were identified. 29 patients had csPCa, and one patient had GS 6. 22 PI-RADS 3 lesions were PSMA-positive (PRIMARY score 3 or more), of which 18 (81.8%) were csPCa on targeted biopsy; 16 PI-RADS 3 lesions were PSMA-negative, of which 4 (25.0%) were csPCa on targeted biopsy (p < 0.001). Sensitivity and specificity for the presence of csPCa on targeted biopsy was 81.8% and 75.0%. Out of 30 patients, 12 (40.0%) had 16 discordant PSMA-avid (PRIMARY score 2 or more) lesions and 10 patients had 10 discordant PSMA-positive lesions outside PI-RADS 3 lesions In 5 of those 12 (41.7%), discordant PSMA-avid lesions had higher PRIMARY score than PI-RADS 3 lesions. In 4 of those 5 (80%), systemic biopsy showed higher GS than targeted biopsy.

Lesion-level analysis showed PSMA-positive PI-RADS 3 lesions had higher probability of csPCa than PSMA-negative PI-RADS 3 lesions. Discordant PSMA-avid lesions with higher PRIMARY score than that of PI-RADS 3 lesions often represented another more aggressive focus not initially identified on MRI.