68Ga-PSMA-11 PET/CT in primary staging of prostate cancer: PSA and Gleason score predict the intensity of tracer accumulation in the primary tumour

Prostate cancer (PC) cells typically show increased expression of prostate-specific membrane antigen (PSMA), which can be visualized by Ga-68-PSMA-11 PET/CT. The aim of this study was to assess the intensity of Ga-68-PSMA-11 uptake in the primary tumour and metastases in patients with biopsy-proven PC prior to therapy, and to determine whether a correlation exists between the primary tumour-related Ga-68-PSMA-11 accumulation and the Gleason score (GS) or prostate-specific antigen (PSA) level. Ninety patients with transrectal ultrasound biopsy-proven PC (GS 6-10; median PSA: 9.7 ng/ml) referred for Ga-68-PSMA-11 PET/CT were retrospectively analysed. PET images were analysed visually and semiquantitatively by measuring the maximum standardized uptake value (SUVmax). The SUVmax of the primary tumour and pathologic lesions suspicious for lymphatic or distant metastases were then compared to the physiologic background activity of normal prostate tissue and gluteal muscle. The SUVmax of the primary tumour was assessed in relation to both PSA level and GS. Eighty-two patients (91.1%) demonstrated pathologic tracer accumulation in the primary tumour that exceeded physiologic tracer uptake in normal prostate tissue (median SUVmax: 12.5 vs. 3.9). Tumours with GS of 6, 7a (3+4) and 7b (4+3) showed significantly lower Ga-68-PSMA-11 uptake, with median SUVmax of 5.9, 8.3 and 8.2, respectively, compared to patients with GS > 7 (median SUVmax: 21.2; p < 0.001). PC patients with PSA >= 10.0 ng/ml exhibited significantly higher uptake than those with PSA levels < 10.0 ng/ml (median SUVmax: 17.6 versus 7.7; p < 0.001). In 24 patients (26.7%), 82 lymph nodes with pathologic tracer accumulation consistent with metastases were detected (median SUVmax: 10.6). Eleven patients (12.2%) revealed 55 pathologic osseous lesions suspicious for bone metastases (median SUVmax: 11.6). The GS and PSA level correlated with the intensity of tracer accumulation in the primary tumours of PC patients on Ga-68-PSMA-11 PET/CT. As PC tumours with GS 6+7 and patients with PSA values <= 10 ng/ml showed significantly lower Ga-68-PSMA-11 uptake, Ga-68-PSMA-11 PET/CT should be preferentially applied for primary staging of PC in patients with GS > 7 or PSA levels >= 10 ng/ml.