Clinical application of PRIMARY score in diagnosing clinically significant prostate cancer: a comparative study using...

The PRIMARY score was developed to standardize the evaluation of intraprostatic prostate-specific membrane antigen (PSMA) activity on gallium-68 (⁶⁸Ga)-PSMA-11 positron emission tomography/computed tomography (PET/CT), but its application to fluorine-18-labeled (¹⁸F)-PSMA-1007 PET/CT remains underexplored. This study aimed to assess the diagnostic performance of the PRIMARY score on both tracers and compare their effectiveness in identifying clinically significant prostate cancer (csPCa).

This retrospective study included 192 patients who underwent PSMA PET/CT and systematic biopsy. PRIMARY scores were categorized as PET-positive (score 3-5) or PET-negative (score 1-2). PSMA uptake patterns were categorized as no pattern, diffuse transition (TZ)/central zone (CZ) (non-focal), focal TZ, or focal peripheral zone (PZ). Diagnostic metrics [sensitivity, specificity, accuracy, positive predictive value (PPV), negative predictive value (NPV)] were calculated against histopathology. DeLong test was used to compare the areas under the receiver operating characteristic (ROC) curves (AUCs) of the PRIMARY score and maximum standardized uptake value (SUVmax). Univariate logistic regression assessed associations between SUVmax and csPCa by pattern, reporting odds ratios (ORs) with 95% confidence intervals (CIs).

The csPCa detection rates were 35.6% (21/59) for ⁶⁸Ga-PSMA-11 PET/CT and 23.3% (31/133) for ¹⁸F-PSMA-1007 PET/CT. When further stratified by PRIMARY score, csPCa was present in 4/35 (11.4%) of patients with scores 1-2 and 17/24 (70.8%) with scores 3-5 for ⁶⁸Ga-PSMA-11, compared with 1/53 (1.9%) and 30/80 (37.5%) for ¹⁸F-PSMA-1007. These differences in csPCa distribution between the two tracers were statistically significant (P<0.001). Using the PRIMARY score, ⁶⁸Ga-PSMA-11 PET/CT demonstrated sensitivity, specificity, accuracy, PPV, and NPV of 80.95%, 81.58%, 81.36%, 70.83%, and 88.57%, respectively, whereas ¹⁸F-PSMA-1007 PET/CT showed 96.77%, 50.98%, 61.65%, 37.50%, and 98.11%, respectively. The ROC analysis for diagnosing csPCa revealed an AUC of 0.915 for ⁶⁸Ga-PSMA-11 PET/CT, higher than that for SUVmax (AUC 0.744, P<0.001), indicating superior diagnostic performance compared with using SUVmax alone. For ¹⁸F-PSMA-1007 PET/CT, the AUCs for the PRIMARY score and SUVmax were 0.833 and 0.811, respectively (P>0.05), indicating that the PRIMARY score provided no diagnostic advantage over SUVmax. In the ¹⁸F-PSMA-1007 PET/CT group, a significant association between SUVmax and csPCa was observed in the focal PSMA pattern (P<0.001), yet no significant association was found in other patterns.

The PRIMARY score improves the diagnostic accuracy for csPCa in ⁶⁸Ga-PSMA-11 PET/CT but does not show the same benefit for ¹⁸F-PSMA-1007 PET/CT. Future research should focus on refining the use of the PRIMARY score in ¹⁸F-PSMA-1007 PET/CT to enhance its overall diagnostic performance.