Diagnostic performance of 68Ga-PSMA PET/CT for restaging prostate cancer

Objectives: The aim of this study is to evaluate 68Ga-PSMA PET/CT for detecting recurrent prostate carcinoma (PCa) in a large cohort of patients with biochemical recurrence (BCR) and to determine the best time for performing 68Ga-PSMA PET/CT scans.

Methods: We retrospectively studied 68Ga-PSMA-11-PET/CT scans of 556 patients with BCR of PCa which had previously been treated for localized cancer. BCR is defined as PSA (prostate-specific antigen) >0.2 ng/ml and rising. The performance of 68Ga-PSMA-11-PET/CT in relation to the PSA value at the time of the scans was assessed by receiver operating characteristic (ROC) curves generating by plotting sensitivity versus 1-specificity.

Results: 68Ga-PSMA-PET/CT revealed malignant prostatic lesions in 418/556 patients (75%). In our series, 93 PSMA-PET/CT scans were performed in patients with PSA levels between 1 and 2 ng/ml with a positivity rate of 73%. In this subpopulation, 68Ga-PSMA-PET/CT showed the presence of distant metastases in 17% (16 of 93) and of oligometastatic disease in 58% (54 of 93). The absolute PSA value at the time of the scan was associated with an increased probability of a positive 68Ga-PSMA-PET/CT scan (p<0.001). By means of ROC analysis a PSA value of 1.40 ng/ml was found to be the optimal cut off-level for predicting positive and negative scans (AUC=0.793; 95% CI 0.752-0.834). In patients with a PSA value <1.40 ng/ml, 53% (115/215) 68Ga-PSMA-PET/CT scans were positive, whereas patients with a PSA ≥1.40 ng/ml exhibited positive scan results in 89% (303/341) (p<0.001, r 0.399). Oligometastatic disease was determined in 44% (95/215) of patients with PSA levels below cut off-level vs. 69% (236/341) of patients with PSA above cut off (p<0.001, r 0.255).

Conclusions: This study demonstrates in a large population of patients, that 68Ga-PSMA-11-PET/CT is an excellent method for restaging PC, even in patients with low PSA levels. The PSA level was the main predictor of a positive scan with an optimal cut off-value of 1.40 ng/ml.