The additive value of Ga-RM26 PET/CT to Ga-PSMA-617 PET/CT in assessing Post-treatment outcomes of ARSIs in mCRPC patients.

[BACKGROUND] Besides its potential as a PET/CT tracer, the Gastrin-Releasing Peptide Receptor (GRPR) has been shown to predict the prognosis of Prostate Cancer (PCa). Herein, we aimed to evaluate the additive ability of Ga-RM26 PET/CT as a tracer to predict the prognosis of patients with metastatic Castration-Resistant Prostate Cancer (mCRPC) following Androgen Receptor Signal Inhibitors (ARSIs) therapy.

[METHODS] This retrospective single-center study involved patients who underwent both Ga-PSMA-617 PET/CT and Ga-RM26 PET/CT scans. Based on the GRPR status of their lesions (positive/negative), the patients were stratified into two cohorts, and their actual prognosis was assessed by comparing their maximum Prostate-Specific Antigen (PSA) response rates and Progression-Free Survival (PFS) durations following ARSI therapy.

[RESULTS] This study involved 44 patients. Among them, 41 and 23 showed PSMA uptake and GRPR uptake, respectively, with 3 exhibiting GRPR uptake alone. The GRPR + group had an median PSA response rate of 37.78% and a median PFS duration of 8.9 months, both of which were significantly lower than those of GRPR- patients, whose corresponding values were 69.39% and 14.37 months, respectively. According to the multivariate analysis results, GRPR status, distant Lymph Node Metastasis (LNM) and PSMA SUVmax of bone metastases lesions were significant predictors of the PSA response rate. Furthermore, the GRPR status and PSMA SUVmax of regional lymph node metastases were significant predictors of PFS.

[CONCLUSION] Compared to GRPR- patients, mCRPC patients with GRPR + lesions exhibited a lower median maximum PSA response rate and a shorter median PFS duration following ARSI treatment, implying a poorer response to therapy and relatively worse prognosis in the latter subgroup.