Correlation of [68Ga]Ga-PSMA PET/CT response and PSA decline in first-line enzalutamide for metastatic castration-resistant prostate cancer patients

Purpose: to assess the utility of response monitoring to enzalutamide by using [68Ga]Ga-PSMA PET in mCRPC patients treated with enzalutamide as first-line therapy. Methods: patients underwent [68Ga]Ga-PSMA PET less than 8 weeks before and 3 months after starting enzalutamide. On the basis of EAU/EANM criteria, patients were categorized as PSMA responders (PET-R) or PSMA non-responders (PET-NR), whilst, based on PSA, they were classified as biochemical responders (PSA-R) or non-responders (PSA-NR). Survival analysis was performed using the Cox regression hazard model and the Kaplan-Meier method. Results: 69 patients were considered fully evaluable. We observed 47.8% of concordance between [68Ga]Ga-PSMA PET and PSA monitoring at 3 months after starting enzalutamide. For discordant cases, the PSA reduction has a weak impact on PFS and a significant impact on OS in PET-NR patients, whilst this change has no impact either for PFS and OS in PET-R ones. Conclusions: [68Ga]Ga-PSMA PET could be a useful imaging tool for monitoring response to enzalutamide in mCRPC patients, being more informative than PSA in this setting, and possibly better guiding clinicians in therapeutic decisions.