Association Between the PRIMARY Score at Staging Prostate-specific Membrane Antigen Positron Emission Tomography and Overall Survival Among Patients with Newly Diagnosed Prostate Cancer: Findings from the International, Multicenter PROMISE Registry

The PRIMARY score was implemented in Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) version 2 to improve accuracy for the diagnosis of clinically significant prostate cancer using prostate-specific membrane antigen (PSMA) positron emission tomography (PET). We reviewed overall survival (OS) for patients who underwent PSMA PET for initial staging to evaluate the prognostic value of PRIMARY in a large, international, multicenter cohort. The cohort comprised 1889 patients who underwent PSMA PET for initial staging of prostate cancer at investigator sites across Europe and Australia between 2012 and 2021. Hazard ratios (HRs) with 95% confidence interval (CI) were calculated for PRIMARY scores to identify predictors of OS. Complete-case head-to-head comparisons were conducted for Prostate Imaging-Reporting and Data System (PI-RADS) versus PRIMARY scores, and cT stage versus PRIMARY scores. We present preliminary findings up to January 31, 2025, when 231 deaths had occurred. PRIMARY score 5 (HR 1.5, 95% CI 1.0-2.3; p = 0.045) was associated with shorter OS. Improvements in C index values confirmed the added prognostic value of the PRIMARY score when combined with PI-RADS or cT stage. PRIMARY score 5 on initial PSMA PET is prognostic for shorter OS. There is ongoing long-term follow-up in the PROMISE registry (NCT06320223, promise-pet.org).