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

PURPOSE: Prostate cancer (PC) cells typically show increased expression of prostate-specific membrane antigen (PSMA), which can be visualized by 68 Ga-PSMA-11 PET/CT. The aim of this study was to assess the intensity of 68 Ga-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 68 Ga-PSMA-11 accumulation and the Gleason score (GS) or prostate-specific antigen (PSA) level.

METHODS: Ninety patients with transrectal ultrasound biopsy-proven PC (GS 6-10; median PSA: 9.7 ng/ml) referred for 68 Ga-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.

RESULTS: 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 68 Ga-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).

CONCLUSIONS: The GS and PSA level correlated with the intensity of tracer accumulation in the primary tumours of PC patients on 68 Ga-PSMA-11 PET/CT. As PC tumours with GS 6+7 and patients with PSA values ≤10 ng/ml showed significantly lower 68 Ga-PSMA-11 uptake, 68 Ga-PSMA-11 PET/CT should be preferentially applied for primary staging of PC in patients with GS >7 or PSA levels ≥10 ng/ml.