Abstract 1382P
Background
PSMA-targeting radioligand therapy (PSMA-RLT) is a treatment option for metastatic castration-resistant prostate cancers (mCRPC). Patient’s selection is based on PSMA-PET positivity but the optimal lesion tracer uptake cut-offs are not defined. Also, intra-patient variability of PSMA expression and FDG uptake in mCRPC metastases may affect the efficacy of PSMA RLT. This study aimed to determine the prevalence of at least one PSMA-/FDG+ PET lesion in mCRPC patients and to determine its impact on decision to undergo PSMA compassionate RLT.
Methods
The Triple-Tracer strategy against Metastatic PrOstate cancer (3TMPO) study (NCT04000776) is a prospective mCRPC PET-imaging trial. One hundred mCRPC patients with progression and showing at least three metastases by conventional imaging were accrued. 68Ga-PSMA-617 and 18F-FDG PET/CT scans were performed within 10 days and analyzed quantitatively. Positivity of a lesion was defined as its SUVpeak being > 1.5 X SUVmean of the liver.
Results
Median age, PSA and number of metastases per patient were 70 years [44 – 87], 50.1 ng/mL [17.9 – 210] and 4 [3 –99], respectively. At inclusion, 9.1, 19.2, 14.1 and 57.6% of patients had received 0, 1, 2 or >2 lines of systemic therapies (excluding castration) for prostate cancer, respectively. At least one PSMA-/FDG+ PET lesion was found in 45% of patients. In patients that received 0, 1, 2 or >2 lines of systemic therapies, the prevalence of at least one PSMA-/FDG+ PET lesion was 11.1, 26.3, 64.3 and 52.6 %, respectively (p=0.007, Cochran-Armitage test). Twenty-five patients underwent subsequent compassionate-access PSMA-RLT. Interestingly, 8 (32.0%) where found to have at least one PSMA-/FDG+ PET lesion by central quantitative blinded analysis.
Conclusions
A significant proportion of mCRPC patients show at least one PSMA-/FDG+ PET lesion and this proportion increases with lines of systemic therapies. Some patients with limited PSMA-/FDG+ disease were still offered compassionate PSMA-RLT. Further studies are needed to determine the significance of PSMA-/FDG+ PET lesions as a biomarker of PSMA-RLT candidacy.
Clinical trial identification
Editorial acknowledgement
The authors wish to thank the Unité de recherche clinique et épidémiologique (URCE) of Centre de recherche du CHUS for their support in the writing of this abstract and specifically Ms Catherine Allard for the statistical assistance.
Legal entity responsible for the study
Université de Sherbrooke.
Funding
Oncopole program was funded by \"Fonds de recherche du Québec-Santé (FRQS)\", Merck, and the Cancer Research Society.
Disclosure
F. Pouliot: Non-Financial Interests, Personal, Advisory Role: Sanofi; Financial Interests, Personal, Advisory Role: Genzyme, Amgen, Astellas, Bayer, Janssen; Financial Interests, Institutional, Research Grant: Astellas. S. Probst: Non-Financial Interests, Personal, Advisory Role: Bayer; Financial Interests, Personal, Invited Speaker: Bayer, AbbVie, Astellas, Isologics, Lantheus, Point Biopharma. All other authors have declared no conflicts of interest.