(UroToday.com) In a moderated poster presentation at the 2022 American Urologic Association Annual Meeting held in New Orleans and virtually, Dr. Mapelli presented work examining novel imaging approaches for patients undergoing primary staging of high-risk prostate cancer prior to radical prostatectomy. Recently, the use of prostate specific membrane antigen (PSMA)-targeted PET-CT or PET-MRI has become recognized as a more sensitive and accurate staging modality than conventional imaging for patients with newly diagnosed high-risk prostate cancer. However, PSMA might still miss micro-metastatic disease. 68Ga-DOTA-RM2 (bombesin) is an alternative radiotracer with promising potential for PET imaging in prostate cancer. However, data are limited thus far. The authors sought to assess the hypothesis that the combined use of PET and MRI with these tracers could improve staging.
The authors enrolled 22 patients with biopsy proven high-risk prostate cancer for this prospective trial (EudraCT: 2018-001034-18). Prior to radical prostatectomy, all patients underwent 68Ga-PSMA PET/MRI and 19 of them underwent 68Ga-DOTA-RM2 PET/MRI within 16 days. The authors performed TNM classification based on imaging findings. Semi-quantitative PET and quantitative MRI parameters were collected. DICE score for each imaging-based region of interest was manually segmented on the primary tumor on 68Ga-DOTA-RM2 PET, 68Ga-DOTA-RM2 PET, and on T2 MRI. Further, gold standard confirmation was performed with assessment for surgical pathological specimens of 14 patients to validate intra-prostatic findings. Fisher’s exact test and Mann-Whitney U test were used to compare groups.
Primary prostate cancer was detected on all imaging modalities in 18 of 19 patients. In 16 of these patients, the site of the primary prostatic lesion was concordant among the three imaging modalities. Seminal vesicle invasion was detected by MRI in 7 patients and by 68Ga-PSMA in 2 patients. 68Ga-DOTA-RM2 did not detect evidence of SVI. Using 68Ga-PSMA, cN1 disease was identified in 7 of 22 patients and bone metastases were identified in 3 of 22 patients. On the basis of 68Ga-DOTA-RM2 PET, pathological focal nodal uptake was detected in 4 of 19 patients while no patients had detection of pathological skeletal uptake. On a per-node basis with histopathological specimens as the gold standard, there was considerable overlap between the imaging approaches.
The authors conclude that the combination of 68Ga-PSMA and 68Ga-DOTA- RM2 PET/MRI may have a synergic role in primary staging of high-risk prostate cancer. However, as a stand-alone modality, 68Ga-DOTA-RM2 PET/MRI was inferior to 68Ga-PSMA PET/MRI in terms of local and distant staging.
Presented by: Paola Mapelli, MD, PhD, IRCCS San Raffaele Scientific Institute