PRIMARY Scoring in 68Ga-PSMA PET/CT: Correlation with Prostate Cancer Risk Groups and Its Potential Impact on Active Surveillance

Objective The PRIMARY scoring system is a scale designed to identify clinically significant intraprostatic malignancies on 68Ga-PSMA PET/CT images. Active surveillance is a management method for patients with low-risk prostate cancer. In this study, we aimed to assess the efficacy of PRIMARY scoring in identifying appropriate candidates for active surveillance based on the distribution within prostate cancer risk groups. Methods The data of 134 patients diagnosed with PCa by biopsy who underwent 68Ga-PSMA PET/CT imaging for post-diagnostic staging purposes were retrospectively analyzed. Age, total PSA, ISUP grade, prostate lesion SUVmax values, PI-RADS scores, and PRIMARY scores were recorded. Patients were classified into low-risk and intermediate/high-risk groups. Results In the intermediate/high-risk group, the PRIMARY score was 1–2 in 17.6% and 3–5 in 82.4% of patients. In the low-risk group, the PRIMARY score was 1–2 in 34.7% and 3–5 in 65.3% of patients. None of the patients in the low-risk group had a PRIMARY score of 5. The most frequent PRIMARY score in both groups was 4, and there was a significant difference between the average SUVmax values of the intermediate/high and low-risk groups with a PRIMARY score of 4 (p = 0.018). The sensitivity of PRIMARY scoring in detecting patients in the intermediate/high-risk group was 82.3%, the specificity was 34.6%, and the positive predictive value (PPV) was 68.6%. When a cut-off SUVmax value 5.0 was used for the PRIMARY score of 4, the sensitivity was 67.0%, the specificity was 65.3% and the PPV was 77.0%. In the ROC analysis, the area under the curve was 0.727 for PRIMARY scoring, 0.662 for PI-RADS, and 0.744 for their combined mean. Conclusion The PRIMARY scoring system can complement PI-RADS scoring in mpMRI for selecting patients suitable for active surveillance. Revising the PRIMARY score 4 with an SUVmax cut-off value may increase the specificity.