68Ga-RM2 is a synthetic bombesin receptor antagonist targeting gastrin-releasing peptide receptors that are overexpressed in several human tumors, including prostate cancer. The molecular structure of gastrin-releasing peptide receptors is as follows:
In this study, men with biochemical recurrence and negative CT/MRI and bone scintigraphy were evaluated for the presence of prostate cancer.
This study enrolled 131 men with biochemically recurrent prostate cancer (n=10 in phase 1, n=21 in phase 2, and n=100 in phase 2/3), with a mean ± SD age of 67.8 ± 7.1 years. The mean ± SD PSA was 4.8 ± 13.3 ng/mL. Imaging started at 40-89 minutes (mean ± SD: 50.7 ± 9.6) after injection of 113.8-151.2 MBq (mean ± SD: 140.3 ± 6.4) of 68Ga-RM2 using a time-of-flight-enabled simultaneous PET/MRI scanner:
All patients had rising PSA and negative conventional imaging prior to enrollment. In the phase 2/3 portion of the study, 69/100 (69%) of patients had a positive scan. The positivity rate of 68Ga-RM2 PET was: 40.7% for PSA < 0.5 ng/dl (n=27), 72.2% for PSA 0.5 – 1.0 ng/dl (n=18), 64.3% for PSA 1.0 – 2.0 ng/dl (n=14), 86.7% for PSA 2.0 – 5.0 ng/dl (n=15) and 88.5% for PSA > 5.0 ng/dl (n=26):
PSA velocity values were 1.9 ± 2.7 ng/ml/year (range: 0-9.1) in patients with negative PET scans and 5.8 ± 9 ng/ml/year (range: 0.2-45.4) in patients with positive PET scans:
Among 20 patients considered for changes in management, 3 patients were downstaged (15%), 7 patients had no change (35%), and 10 patients were upstaged (50%). As follows is a representative image of a 68Ga-RM2 PET/MRI scan in a patient with a PSA of 1.32 ng/mL:
Dr. Iagaru concluded his presentation of 68Ga-RM2 PET/MRI in patients with biochemically recurrent prostate cancer with the following summary points:
- 68Ga-RM2 PET/MRI identifies gastrin-releasing peptide receptor expression in biochemically recurrent prostate cancer lesions despite negative conventional imaging, indicating it is a promising PET radiopharmaceutical in this clinical scenario
- 68Ga-RM2 may identify higher-risk patients given the highly statistically significant difference PSA velocity values between patients with negative and positive scans and maybe a complementary radiopharmaceutical to the PSMA-targeting tracers to ultimately allow for personalized medicine
Presented by: Andrei Iagaru, MD, Professor of Radiology - Nuclear Medicine and the Chief of the Division of Nuclear Medicine and Molecular Imaging at Stanford Health Care. Stanford University, Palo Alto, CA
Co-Authors: Lucia Baratto, Hong Song, Heying Duan, Farshad Moradi, Guido Davidzon
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2021 American Urological Association, (AUA) Annual Meeting, Fri, Sep 10, 2021 – Mon, Sep 13, 2021.