The PRIMARY Scoring System on PSMA PET for Clinically Significant Prostate Cancer Detection

PURPOSE OF THE REPORT: The PRIMARY score standardizes interpretation of PSMA PET for intraprostatic assessment of clinically significant prostate cancer (csPCa). Although early studies are promising, no meta-analysis has systematically evaluated its accuracy. We aimed to assess the diagnostic performance of PRIMARY and compare it with PI-RADS. MATERIAL AND METHODS: A systematic review and meta-analysis were performed according to PRISMA-DTA guidelines. Studies assessing the PRIMARY score on PSMA PET/CT or PET/MRI for csPCa detection were included. The primary analysis focused on biopsy-naïve patients; secondary analyses incorporated all studies irrespective of prior histology, evaluated thresholds (≥3 vs. ≥4), compared PRIMARY with PI-RADS, and examined combined performance. Pooled sensitivity and specificity were estimated with a bivariate random-effects model. RESULTS: Thirteen studies (n=1974) were included. In biopsy-naïve cohorts (6 studies), PRIMARY ≥3 achieved pooled sensitivity/specificity of 90% (95% CI: 86%-93%) and 63% (95% CI: 57%-69%). In an expanded analysis of 9 studies regardless of prior biopsy, values were 87% (82%-90%) and 56% (46%-65%). Across 5 studies directly comparing thresholds, raising the cutoff from ≥3 to ≥4 reduced sensitivity from 89% to 81% but increased specificity from 53% to 72%. Three head-to-head studies showed comparable accuracy between PRIMARY and PI-RADS. CONCLUSIONS: PRIMARY demonstrates high sensitivity and moderate specificity for csPCa, comparable to PI-RADS. In biopsy-naïve men it shows robust performance, and combination with mpMRI further improves sensitivity. Threshold selection should reflect clinical intent, supporting PRIMARY as a tool for pre-biopsy risk stratification and integrated diagnostic workflows.