Primary Score as a Predictive Marker in Intermediate-Risk Prostate Cancer: Insights from PSMA PET/CT Imaging

Purpose: This study aimed to determine whether the PRIMARY Score on prostate specific membrane antigen (PSMA) positron emission tomography/compute tomography (PET/CT) can predict adverse pathology and prognosis in patients with intermediate-risk prostate cancer (PCa). Materials and methods: This is a retrospective, multicenter analysis of patients diagnosed with intermediate risk PCa. Patients were staged using pelvic multiparametric magnetic resonance imaging (mpMRI) and radiolabeled PSMA PET/CT, either [68 Ga]Ga-PSMA-11 or [18F]F-PSMA1007, to evaluate the extent of disease before initiating appropriate treatment. PI-RADS Version 2.1 and PRIMARY score were used for a quantitative analysis, respectively for mpMRI and PSMA PET/CT. Biochemical recurrence of disease was defined as a post-operative serum PSA > 0.2 ng/ml on two separate occasions at minimum 2-week intervals. Results: Seventy-eight intermediate-risk PCa patients were enrolled. PRIMARY scores > 3 was found in 62% of favorable (n = 50) and 71% of unfavorable cases (n = 28). Gleason score changes occurred in 20% of favorable-risk patients, with 90% having a PRIMARY score > 3. Biochemical recurrence was observed in 17% of patients during follow-up, predominantly among favorable-risk cases (13%), where most had Gleason score changes and a PRIMARY score > 3. Conclusions: These results highlight the predictive value of the PRIMARY score for Gleason score changes.