Pilot Comparison of 68Ga-RM2 PET and 68Ga-PSMA PET in Patients with Biochemically Recurrent Prostate Cancer (original) (raw)

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. SUV max and SUV mean 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 gastrinreleasing peptide receptors in different types of prostate cancer.