Abstract
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Objectives: 68Ga-RM2 is a synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptors (GRPRs). GRPRs are highly overexpressed in several human tumors, including prostate cancer (PC). In this study we evaluated 68Ga-RM2 PET/CT in patients with newly diagnosed intermediate- or high-risk PC.
Methods: We enrolled 34 men, 50-78 years-old (mean±SD: 62.9±7.1). Images were acquired 42-72 minutes (mean±SD: 54.0±6.7) after injection of 3.3-6.7 mCi (mean±SD: 3.8±0.6) of 68Ga-RM2. 68Ga-RM2 PET/CT findings were compared to concurrent preoperative pelvic mpMRI (n=29) and 68Ga-PSMA11 PET (n=13). Findings were also correlated with pre-scan prostate saturation biopsy (n=34) and post-prostatectomy whole-mount pathology (n=27). Seven participants decided to undergo radiation therapy.
Results: The cohort included 13 participants with intermediate-risk and 21 participants with high-risk PC, with PSA 3.3-504 ng/ml (mean±SD: 24.6±84.9) at diagnosis. Preoperative 68Ga-RM2 PET identified intraprostatic cancer foci in 33 patients (57 lesions), whereas mpMRI alone identified PIRADS 4 or 5 lesions in 26/29 patients (34 lesions vs. 44 lesions on 68Ga-RM2 PET) and PIRADS 3 in 3/29 patients (5 lesions vs. 4 lesions on 68Ga-RM2 PET). mpMRI was negative in 2/29 patients (3 lesions on 68Ga-RM2 PET). 68Ga-RM2 PET demonstrated focal uptake in non-enlarged pelvic lymph nodes in 4 patients. Final pathology confirmed nodal metastases in 3 patients and follow-up imaging confirmed nodal metastasis in 1 patient. One patient with normal pelvic nodes on PET/CT had nodal metastases on post-surgery histopathology. 68Ga-RM2 PET and 68Ga-PSMA11 PET done 1-12 days (mean±SD: 3.7±3.8) apart identified 23 and 21 intraprostatic lesions, respectively, as well as 4 and 5 pelvic lymph nodes, respectively. Non-congruent findings between 68Ga-RM2 PET and 68Ga-PSMA11 PET were recorded in 4/13 patients (intraprostatic lesions in 3 patients and nodal lesion in 1 patient).
Conclusions: Our preliminary results suggest that 68Ga-RM2 PET can accurately detect intermediate- and high-risk prostate cancer. In addition, it appears to have better performance when compared to mpMRI and similar performance to 68Ga-PSMA11 PET. These findings need to be confirmed in larger studies.