Prospective Evaluation of 68Ga-RM2 PET/MRI in Patients with Biochemical Recurrence of Prostate Cancer and Negative Findings on Conventional Imaging

Ga-68-labeled DOTA-4-amino-1-carboxymethyl-piperidine-D-Phe-GlnTrp- Ala-Val-Gly-His-Sta-Leu-NH2 (Ga-68-RM2) is a synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptor (GRPr). GRPr proteins are highly overexpressed in several human tumors, including prostate cancer (PCa). We present data from the use of Ga-68-RM2 in patients with biochemical recurrence (BCR) of PCa and negative findings on conventional imaging. Methods: We enrolled 32 men with BCR of PCa, who were 59-83 y old (mean +/- SD, 68.7 +/- 6.4 y). Imaging started at 40-69 min (mean, 50.5 +/- 6.8 min) after injection of 133.2-151.7 MBq (mean, 140.6 +/- 7.4 MBq) of (68)GaRM2 using a time-of-flight-enabled simultaneous PET/MRI scanner. T1-weighted, T2-weighted, and diffusion-weighted images were acquired. Results: All patients had a rising level of prostate-specific antigen (PSA) (range, 0.3-119.0 ng/mL; mean, 10.1 +/- 21.3 ng/mL) and negative findings on conventional imaging (CT or MRI, and a Tc-99m-methylene diphosphonate bone scan) before enrollment. The observed Ga-68-RM2 PET detection rate was 71.8%. Ga-68-RM2 PET identified recurrent PCa in 23 of the 32 participants, whereas the simultaneous MRI scan identified findings compatible with recurrent PCa in 11 of the 32 patients. PSA velocity was 0.32 +/- 0.59 ng/mL/y (range, 0.04-1.9 ng/mL/y) in patients with negative PET findings and 2.51 +/- 2.16 ng/mL/y (range, 0.13-8.68 ng/mL/y) in patients with positive PET findings (P 5 0.006). Conclusion: Ga-68-RM2 PET can be used for assessment of GRPr expression in patients with BCR of PCa. High uptake in multiple areas compatible with cancer lesions suggests that Ga-68-RM2 is a promising PET radiopharmaceutical for localization of disease in patients with BCR of PCa and negative findings on conventional imaging.