A Pilot Study of ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI for Biopsy Guidance in Patients with Suspected Prostate Cancer

Targeting of lesions seen on multiparametric MRI (mpMRI) improves prostate cancer (PC) detection at biopsy. However, 20%-65% of highly suspicious lesions on mpMRI (PI-RADS [Prostate Imaging-Reporting and Data System] 4 or 5) are false-positives (FPs), while 5%-10% of clinically significant PC (csPC) are missed. Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptors (GRPRs) are both overexpressed in PC. We therefore aimed to evaluate the potential of ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI for biopsy guidance in patients with suspected PC. Methods: A highly selective cohort of 13 men, aged 58.0 ± 7.1 y, with suspected PC (persistently high prostate-specific antigen [PSA] and PSA density) but negative or equivocal mpMRI results or negative biopsy were prospectively enrolled to undergo ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI. PET/MRI included whole-body and dedicated pelvic imaging after a delay of 20 min. All patients had targeted biopsy of any lesions seen on PET followed by standard 12-core biopsy. The SUV_max of suspected PC lesions was collected and compared with gold standard biopsy. Results: PSA and PSA density at enrollment were 9.8 ± 6.0 (range, 1.5-25.5) ng/mL and 0.20 ± 0.18 (range, 0.06-0.68) ng/mL², respectively. Standardized systematic biopsy revealed a total of 14 PCs in 8 participants: 7 were csPC and 7 were nonclinically significant PC (ncsPC). ⁶⁸Ga-PSMA11 identified 25 lesions, of which 11 (44%) were true-positive (TP) (5 csPC). ⁶⁸Ga-RM2 showed 27 lesions, of which 14 (52%) were TP, identifying all 7 csPC and also 7 ncsPC. There were 17 concordant lesions in 11 patients versus 14 discordant lesions in 7 patients between ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET. Incongruent lesions had the highest rate of FP (12 FP vs. 2 TP). SUV_max was significantly higher for TP than FP lesions in delayed pelvic imaging for ⁶⁸Ga-PSMA11 (6.49 ± 4.14 vs. 4.05 ± 1.55, P = 0.023) but not for whole-body images, nor for ⁶⁸Ga-RM2. Conclusion: Our results show that ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI are feasible for biopsy guidance in suspected PC. Both radiopharmaceuticals detected additional clinically significant cancers not seen on mpMRI in this selective cohort. ⁶⁸Ga-RM2 PET/MRI identified all csPC confirmed at biopsy.