Detection of prostate cancer with the [68Ga]-labeled bombesin antagonist RM2 in patients undergoing radical prostatectomy.

Abstract

80 Background: Gastrin-releasing-peptide receptor (GRPr) is overexpressed in prostate carcinoma (PCa) and offer new means to detect prostate cancer. The bombesin derivative RM2 (DOTA-4-amino-1-carboxymethylpiperidine-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2) is a GRPr antagonist with high binding affinity (Kd 3 nM). A first-in-man study was performed to assess tumor targeting potential of [68Ga]RM2 in patients with local PCa using PET/CT. Based on promising results a Phase I/II study in local PCa was initiated. Methods: In the initial study eleven men with biopsy-proven PCa scheduled for radical prostatectomy were enrolled. The patients (pt) received an i.v. dose of 140 MBq of [68Ga]RM2 followed by dynamic imaging for at least 60 min p.i. The PET assessment included visual evaluation of [68Ga]RM2 intra-prostatic and nodal uptake as well as quantification. An ongoing Phase I/II study is designed to enroll 30+50 biopsy-positive PCa patients. The initial 30 pt have been enrolled, stratified into high, intermediate and low risk of prostate Ca recurrence as defined by NCCN criteria. Results: High uptake of [68Ga]RM2 is seen in pancreas and the urinary system with low background in the rest of the body. Despite of high bladder activity focal or multifocal intraprostatic uptake was detectable. In the first study 10 of 11 pt had positive scans. Subsector analysis of PET positivity vs. pathology yielded a sensitivity, specificity and accuracy of 89, 81, and 83%, respectively. SUVmax was measured in 14 lesions from 9 pts, classified in two groups according to postoperative Gleason score (GS). The higher GS group showed a trend toward higher SUV-values, 10.0 ± 6.7 vs. 6.2 ± 2.5 (t-test: t = -1.21, p-value = 0.28). Both of which were elevated compared to normal tissue 1.2 ± 0.8 The ongoing study is designed with a power of 95% to discriminate between the two GS groups with statistical significance (p = 0.05). Conclusions: [68Ga]RM2 is a promising new tracer with a high detection rate for PCa. Preliminary data indicates higher uptake in more aggressive cancers. The current study is assessing the diagnostic accuracy and impact of presurgical risk assessment on tumor detection in newly diagnosed PCa patients. Clinical trial information: NCT02483884.