Patients With Biochemical Recurrence of Prostate Cancer: Ga-68–RM2 PET-MRI vs MRI Alone for Lesion Detection

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In a single-center phase II/III imaging trial reported in The Lancet Oncology, Duan and colleagues found that gallium Ga-68–labeled RM2 (Ga-68–RM2) positron-emission tomography (PET)-magnetic resonance imaging (MRI) outperformed MRI alone in positive findings and number of lesions detected in patients with biochemical recurrence of prostate cancer.

As stated by the investigators, “National Comprehensive Cancer Network guidelines include prostate-specific membrane antigen (PSMA)-targeted PET for detection of biochemical recurrence of prostate cancer. However, targeting a single tumor characteristic might not be sufficient to reflect the full extent of disease. Gastrin-releasing peptide receptors (GRPR) have been shown to be overexpressed in prostate cancer. In this study, we aimed to evaluate the diagnostic performance of the GRPR-targeting radiopharmaceutical [Ga-68–RM2] in patients with biochemical recurrence of prostate cancer.”

Study Details

The study included 100 patients enrolled at Stanford University between December 2015 and July 2021. All had noncontributory conventional imaging (computed tomography or bone scintigraphy). All patients underwent Ga-68–RM2 PET-MRI and MRI alone. The primary outcome was the proportion of patients with positive findings on Ga-68–RM2 PET-MRI vs MRI alone after initial therapy. The primary outcome was considered met if ≥ 30% of patients had at least one lesion detected by Ga-68–RM2 PET-MRI and the number of lesions detected by Ga-68–RM2 PET-MRI was significantly greater than MRI alone.

Key Findings

The primary outcome measure was satisfied. Ga-68–RM2 PET-MRI was positive in 69 patients (69%) and MRI alone was positive in 40 patients (40%; P < .0001). The number of lesions detected was 143 with Ga-68–RM2 PET-MRI vs 96 with MRI (P < .0001).

No grade ≥ 1 adverse events were reported.

The investigators concluded, “[Ga-68–RM2] PET–MRI showed better diagnostic performance than MRI alone in patients with biochemical recurrence of prostate cancer. Further prospective comparative studies with PSMA-targeted PET are needed to gain a better understanding of GRPR and PSMA expression patterns in these patients.”

Andrei Iagaru, MD, of the Department of Radiology, Division of Nuclear Medicine and Molecular Imaging, Stanford University, is the corresponding author for The Lancet Oncology article.

Disclosure: The study was funded by the U.S. Department of Defense. For full disclosures of the study authors, visit

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