⁶⁸Ga-PSMA PET/CT for primary diagnosis of prostate cancer in men with contraindications to or negative mpMRI

Background: ⁶⁸Ga-PSMA PET/CT may represent the most promising imaging modality for identification and risk stratification of prostate cancer (PCa) in patients with contraindications to or negative multiparametric MRI (mpMRI).

Methods: This prospective observational study analyzed ⁶⁸Ga-PSMA PET/CT in a selected group of patients with persistently elevated PSA and/or PHI (prostate health index) suspicious for PCa, negative digital rectal examination, and at least one negative biopsy. The cohort comprised men with either an equivocal mpMRI (PI-RADSv2. &#8804;2) or an absolute or relative contraindication to mpMRI. All patients underwent ⁶⁸Ga-PSMA PET/CT 60 minutes after radiopharmaceutical injection (185-250MBq). Focal uptake superior to background activity was considered positive and selected for target biopsy. Sensitivities, specificities, and confidence intervals (CIs) were calculated compared to histopathology. ROC analysis was applied to determine optimal cut-off values of ⁶⁸Ga-PSMA uptake for the identification of clinically significant PCa (Gleason score ≥7). Results: Out of 610 consecutive patients enrolled, from January to August 2017 45 patients (mean age 63 years) were referred to ⁶⁸Ga-PSMA PET/CT. The mean PSA value was 10.46 ng/ml and mean PHI 43.02. Twenty-five subjects (55.5%) were considered having a positive PET and underwent software assisted fusion target biopsy. The overall number of regions of interest (ROIs) was 34, and the median number of ROIs was 1 (1-3). The overall PCa detection rate was 44% (11/25). The total number of target cores was 90 and the total number of positive core was 25 (27.8%). Uptake values of ROIs detected on ⁶⁸Ga-PSMA PET were as follows: median SUV_max 5.34 (range 2.25-30.41), median background SUV 2.69 (range 1.61-3.62), and ratio of SUV_max to background SUV (SUV_ratio) 1.99 (range 1.06-14.42). Mean and median uptake values on ⁶⁸Ga-PSMA PET (i.e. SUV_max or SUV_ratio) were significantly higher in the case of GS 7 lesions than in GS 6 or benign lesions (p<0.001). On ROC analysis, a SUV_max of 5.4 and a SUV_ratio of 2 could discriminate clinically relevant PCa with an overall sensitivity of 100% in both cases and a specificity of 76% and 88%, respectively.

Conclusions: Our findings support the use of ⁶⁸Ga-PSMA PET/CT for primary detection of PCa in a specific subset of men. Its capacity to detect clinically relevant PCa in patients with equivocal or negative mpMRI could offer a further imaging option in this selected population.