Prospective evaluation of the PRIMARY score using [18F]PSMA-1007 PET/MRI in second-line prostate biopsies after negative MRI

Abstract Purpose PSMA PET has been proposed for guiding targeted prostate biopsies. As the rate of clinically significant prostate cancer (csPCa) is positively correlated with PSA density (PSAd), a potential application for PSMA-guided biopsies may be men with negative MRI-first (PI-RADS-1-2) but increased PSAd. The PRIMARY scoring system, using the intraprostatic PSMA-pattern was developed and tested using [ 68 Ga]Ga-PSMA-11 and proposed to be universal across PSMA-ligands, however no data on [ 18 F]PSMA-1007 for biopsy guidance exists. Thus, the aim of this study was to evaluate the PRIMARY score for prostate biopsy guidance using [ 18 F]PSMA-1007 in a prospective clinical setup. Methods 91 patients were prospectively enrolled for [ 18 F]PSMA-1007 PET/MRI, 86 of these for biopsy guidance after negative MRI or non-csPCa biopsies from PI-RADS 3–5 lesions and persistent suspicion of csPCa. Transperineal MRI/ultrasound fusion target biopsies were performed predominantly from PRIMARY 3–5 lesions. Nine patients with PRIMARY 1–2 did not undergo target biopsies. CsPCa was defined as ISUP grade ≥ 2. Results In a per patient analysis, 23.3% (20/86) were diagnosed with csPCa. In line with previous studies, the rate of csPCa increased with higher PRIMARY score in a per lesion analysis, constituting 0% (0/1), 0% (0/8), 7.2% (7/97), 60% (15/25), and 60% (6/10) for PRIMARY 1, 2, 3, 4, and 5 lesions, respectively. The 7.2% PRIMARY-3 lesions containing csPCa exhibited common characteristics such as anterior location or lack of well-defined separation from the peripheral zone. Conclusion We evaluated the PRIMARY score for use with [¹⁸F]PSMA-1007 and identified benign features and potential “red flags” for PRIMARY-3 lesions. We found csPCa in 23.3% of patients with negative MRI or non-csPCa biopsies from PI-RADS 3–5 lesions and persistent suspicion of csPCa.