Results of First Interim Analysis of 68Ga-NeoB and 68Ga-PSMA R2 PET/MRI in Patients with Biochemically Recurrent Prostate Cancer

Introduction: Novel radiopharmaceuticals are evaluated for the diagnosis of biochemically recurrent prostate cancer (BCR PC). Here, we compare the gastrin releasing peptide receptors (GRPR) - targeting ⁶⁸Ga-NeoB with the prostate specific membrane antigen (PSMA) – targeting ⁶⁸Ga-PSMA R2.

Methods: Twenty-six patients with BCR PC after initial treatment underwent both ⁶⁸Ga-NeoB PET/MRI and ⁶⁸Ga-PSMA R2 PET/MRI within 2 weeks of each other. ⁶⁸Ga-NeoB imaging started 43-77 minutes (mean±SD: 49.6±7.5) after injection of 145.1-245.6 MBq (mean±SD: 198.6±26.3). ⁶⁸Ga-PSMA R2 imaging started at 44-55 minutes (mean±SD: 47.0±2.9) after injection of 108.4-228.6 MBq (mean±SD: 187.8±29.1). Maximum standardized uptake values (SUV_max) were collected for all detectable lesions. Vital signs (HR, BP) were collected before injecting the radiopharmaceuticals and after the scans. Adverse events were collected up to 24-72 hours after each scan. Scan findings where compared with follow-up imaging and tissue sampling done as standard of care.

Results: PSA ranged 0.3-13.5 ng/ml (mean±SD: 3.1±3.8) in the overall cohort. PSA ranged 0.3-6.5 ng/ml (mean±SD: 1.3±2.1) in patients with negative ⁶⁸Ga-NeoB (n=8) and 0.3-13.5 ng/ml (mean±SD: 3.9±4.2 ) in patients with positive ⁶⁸Ga-NeoB (n=18) (P: 0.11). PSA ranged 0.3-9.3 ng/ml (mean±SD: 2.0±3.0) in patients with negative ⁶⁸Ga-PSMA R2 (n=11) and 0.3-13.5 ng/ml (mean±SD: 3.9±4.2) in patients with positive ⁶⁸Ga-PSMA R2 (n=15) (P: 0.21). Differences in PSA values between negative ⁶⁸Ga-NeoB and ⁶⁸Ga-PSMA R2, as well as between positive ⁶⁸Ga-NeoB and ⁶⁸Ga-PSMA R2 were not statistically significant (P: 0.58 and 0.99, respectively).

⁶⁸Ga-NeoB identified lesions in 3 patients with negative ⁶⁸Ga-PSMA R2. 30 lesions in 18 patients and 20 lesions in 15 patients were detected by ⁶⁸Ga-NeoB PET and ⁶⁸Ga-PSMA R2 PET, respectively. The mean SUV_max ranged 2.9-13.2 (mean±SD: 6.6±3.2) for ⁶⁸Ga-NeoB PET and 2.6-8.8 (mean±SD: 4.4±1.5) for ⁶⁸Ga-PSMA R2 (P=0.019). 8 of the 26 patients had negative ⁶⁸Ga-NeoB and negative ⁶⁸Ga-PSMA R2 (no lesions identified on either scan).

There were no significant changes in vital signs before and after the scans. No adverse events were reported by the participants in the 24-72 hours period after the scans.

Conclusions: Both ⁶⁸Ga-NeoB PET and ⁶⁸Ga-PSMA R2 are safe radiopharmaceuticals that should continue to be evaluated for BCR PC. Identifying patients for whom these two classes of radiopharmaceuticals are complementary may ultimately allow for personalized medicine. Further evaluation in larger cohorts is needed to confirm this preliminary data.