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Clinical Trial
. 2016 Apr;57(4):557-62.
doi: 10.2967/jnumed.115.168393. Epub 2015 Dec 10.

Pilot Comparison of ⁶⁸Ga-RM2 PET and ⁶⁸Ga-PSMA-11 PET in Patients With Biochemically Recurrent Prostate Cancer

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Clinical Trial

Pilot Comparison of ⁶⁸Ga-RM2 PET and ⁶⁸Ga-PSMA-11 PET in Patients With Biochemically Recurrent Prostate Cancer

Ryogo Minamimoto et al. J Nucl Med. .
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Abstract

Glu-NH-CO-NH-Lys-(Ahx)-[(68)Ga(HBED-CC)] ((68)Ga-PSMA-11) is a PET tracer that can detect prostate cancer relapses and metastases by binding to the extracellular domain of PSMA. (68)Ga-labeled DOTA-4-amino-1-carboxymethyl-piperidine-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 ((68)Ga-RM2) is a synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptors. We present pilot data on the biodistribution of these PET tracers in a small cohort of patients with biochemically recurrent prostate cancer.

Methods: Seven men (mean age ± SD, 74.3 ± 5.9 y) with biochemically recurrent prostate cancer underwent both (68)Ga-PSMA-11 PET/CT and (68)Ga-RM2 PET/MRI scans. SUVmax and SUVmean were recorded for normal tissues and areas of uptake outside the expected physiologic biodistribution.

Results: All patients had a rising level of prostate-specific antigen (mean ± SD, 13.5 ± 11.5) and noncontributory results on conventional imaging. (68)Ga-PSMA-11 had the highest physiologic uptake in the salivary glands and small bowel, with hepatobiliary and renal clearance noted, whereas (68)Ga-RM2 had the highest physiologic uptake in the pancreas, with renal clearance noted. Uptake outside the expected physiologic biodistribution did not significantly differ between (68)Ga-PSMA-11 and (68)Ga-RM2; however, (68)Ga-PSMA-11 localized in a lymph node and seminal vesicle in a patient with no abnormal (68)Ga-RM2 uptake. Abdominal periaortic lymph nodes were more easily visualized by(68)Ga-RM2 in two patients because of lack of interference by radioactivity in the small intestine.

Conclusion: (68)Ga-PSMA-11 and (68)Ga-RM2 had distinct biodistributions in this small cohort of patients with biochemically recurrent prostate cancer. Additional work is needed to understand the expression of PSMA and gastrin-releasing peptide receptors in different types of prostate cancer.

Trial registration: ClinicalTrials.gov NCT02440308 NCT02488070.

Keywords: 68Ga; PET/CT; PET/MRI; PSMA; RM2; prostate cancer.

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