68Ga-PSMA PET/CT Versus PSA Monitoring for mCRPC: Survival Following Enzalutamide

The use of ⁶⁸Ga prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA PET/CT) as a diagnostic and monitoring tool has been increasing for patients with prostate cancer.

At the 2024 American Society of Clinical Oncology Annual Meeting, Emilio Francesco Giunta, MD, presented new data comparing patient response to ⁶⁸Ga with prostate-specific antigen (PSA) response in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with enzalutamide as a first-line therapy.

An observational, prospective study comprised 70 patients with mCRPC from October 2017 to May 2022. Each patient was treated with first-line enzalutamide 160 mg once daily and underwent ⁶⁸Ga-PSMA PET/CT within 3 weeks before treatment initiation (baseline) and 12 weeks (SD: ±4 weeks) after initiation.

Data measured at both time points included the sum of metabolic total volume (sMTV), mean and maximum standardized uptake volume (sSUVmean and sSUVmax, respectively), and total lesion activity (sTLA; the product of MTV and SUVmean), for a maximum of 20 lesions.

Patients were categorized as PSMA responders (in case of complete/partial response or stable disease) or PSMA nonresponders (in case of progressive disease), as well as biochemical responders (in case of PSA decrease ≥50%) or biochemical nonresponders (in all other cases). Survival analysis was performed using the Cox regression hazard model and the Kaplan-Meier method.

Upon the data cutoff in December 2023, 69 patients were fully evaluable. The median follow-up was 57 months. The median age of the patient group was 75 years. The Gleason score  was <8 in 24 patients (35%) and ≥8 in 37 (53%). The median baseline PSA was 2.57 µg/L.

The median sSUVmax was 41.6, median sSUVmean was 28.2, and median sTLA was 44.8. Between discordant groups, differences between median progression-free survival (mPFS; P=.09) and median overall survival (mOS; P=.41) were not statistically significant. Upon multivariate analysis, only sTLA at 12 weeks was significantly associated with both mPFS (P=.0004) and mOS (P=.0006).

The use of ⁶⁸Ga-PSMA PET/CT appears to be more accurate than PSA monitoring in predicting survival following enzalutamide initiation in patients with mCRPC.