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

Introduction: <InvalidTag charset="UTF-8" />Targeting of lesions seen on prostate multiparametric MRI (mpMRI) improves prostate cancer (PC) detection at biopsy. However, 20-65% of highly suspicious lesions on mpMRI (PIRADS 4 or 5) prove to be false positives (FP) while 5-10% of clinically significant cancers are missed. Prostate specific membrane antigen (PSMA) and gastrin-releasing peptide receptors (GRPR) are both overexpressed in PC. We therefore aimed to evaluate the potential utility of ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI for biopsy guidance in patients with suspected PC.

Methods: Eleven men, aged 59.9±4.9 years, with suspected PC were prospectively enrolled to undergo ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI, including mpMRI. The prostate was divided into 12 segments (apex lateral, apex medial, base lateral, base medial, mid lateral, mid medial, left and right, respectively) using PET/MRI data. Maximum standardized uptake values (SUV_max) of suspected PC lesions was collected. Biopsies included 1 core through each of the 12 segments and targeted sampling of any lesions seen on PET. PET/MRI results were compared to the gold standard biopsy.

Results: Prostate specific antigen (PSA) and PSA density at the time of PET/MRI were 11.69±6.37 ng/mL and 0.24±0.16 ng/mL², respectively. ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI each identified 26 lesions, whereas 7 lesions in 5 patients were incongruent. PET/MRI guided biopsy led to the additional finding of 6 clinically significant cancers with Gleason score greater or equal to 7 (of which 3 were not seen on mpMRI) and 3 Gleason score 6 lesions (2 were missed by mpMRI). Median SUV_max for true positive (TP) lesions were significantly higher for ⁶⁸Ga-RM2 (9.72±10.95 vs. 7.38±3.60 [P=0.02]) but not for ⁶⁸Ga-PSMA11 (6.57±7.72 vs. 4.54±1.52 [P=0.23]). Sensitivity and specificity for ⁶⁸Ga-RM2 and ⁶⁸Ga-PSMA11 were 75% and 64%, 46% and 86%, respectively, while mpMRI showed the lowest sensitivity at 43% and the highest specificity at 95%.

Conclusions: Our preliminary results show that both ⁶⁸Ga-PSMA11 and ⁶⁸Ga-RM2 PET/MRI are not only feasible for biopsy guidance in suspected PC, but identified additional clinically significant cancers not seen on mpMRI. However, larger studies are needed to shed light on the different expression patterns of PSMA and gastrin releasing peptide receptor in PC.