Abstract
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Purpose: 68Ga-RM2 is a synthetic bombesin receptor antagonist targeting gastrin-releasing peptide receptors (GRPr) that are overexpressed in several human tumors, including prostate cancer (PC). We present data from the use of 68Ga-RM2 in patients with biochemically recurrent (BCR) PC and negative conventional imaging (CI).
Methods: We enrolled 84 men with BCR PC, 59-83 year-old (mean±standard deviation (SD): 69.5±5.8). Imaging started at 40-89 minutes (mean±SD: 51.8±9.1 after injection of 127.5-152.6 MBq (mean±SD: 141.6±5.2) of 68Ga-RM2 using a time-of-flight (TOF)-enabled simultaneous positron emission tomography (PET) / magnetic resonance imaging (MRI) scanner. T1-weighted (T1w), T2-weighted (T2w) and diffusion-weighted images (DWI) were acquired.
Results: All patients had rising prostate specific antigen (PSA) (range: 0.2-124 ng/mL; mean±SD: 8.0±9.4) and negative CI (CT or MRI, and 99mTc MDP bone scan) prior to enrollment. The observed 68Ga-RM2 PET detection rate was 70.2% (50% for PSA < 1 ng/mL, 70% for PSA 1-2 ng/mL, 80% for PSA 2-5 ng/mL and 90.3% for PSA > 5 ng/mL. 68Ga-RM2 PET identified recurrent PC in 59 of the 84 participants, while the simultaneous MRI scan identified findings compatible with recurrent PC in 25 of the 84 patients. PSA velocity (PSAv) values were 0.29±0.44 ng/ml/year (range: 0.03-1.9) in patients with negative PET scans and 2.29±2.01 ng/ml/year (range: 0.13-8.68) in patients with positive PET scans (P: 0.0042).
Conclusions: 68Ga-RM2 PET identifies GRPr expression in BCR PC lesions despite negative CI, confirming it as a promising PET radiopharmaceutical in this clinical scenario. 68Ga-RM2 may identify higher risk patients given the highly statistically significant difference PSA velocity values between patients with negative and positive scans.
