Primary lymph-node staging with 68 Ga-PSMA PET in high-risk prostate cancer: pathologic correlation with extended pelvic lymphadenectomy specimens

This study aims to assess the diagnostic efficacy of Gallium-68-prostate-specific membrane antigen positron emission tomography (PET)/computed tomography (CT) (68Ga PSMA PET-CT) in primary nodal staging of high-risk prostate cancer (PCa) when compared to pathologic findings of extended pelvic lymph-node dissection (eLND). The records of high-risk PCa patients who were preoperatively staged through 68Ga PSMA PET-CT and who underwent robot-assisted radical prostatectomy with eLND either alone or as part of multimodal definitive therapy between August 2016 and November 2019 were retrospectively reviewed. Surgeons were not blinded to the results of the 68Ga PSMA PET-CT scan. Pathologic uptake was defined as any anomalous uptake which was not better explained by another cause and was suggestive of PCa. The reference standard for this study was the pathologic confirmation using a node-based analysis. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for 68Ga PSMA PET-CT were calculated in a per-patient analysis using IBM SPSS Statistics version 25. Seventeen patients met the selection criteria. Mean age was 63 years (range 44-77) and mean and median preoperative serum prostate specific antigen was 19.25 and 9 ng/ml (range 6-131), respectively. The most common pathologic Gleason score was 8 (52.9% of cases). Seven patients (41%) had positive surgical margins and were submitted to adjuvant radiotherapy. Mean number of per patient removed lymph-nodes was 13 (±2.19). 68Ga PSMA PET-CT showed findings compatible with lymph node metastases in 4/17 patients and with locally-confined disease in 13/17 patients. Following pathologic confirmation, the per-patient sensibility of the 68Ga PSMA PET-CT was calculated at 75% (1 false negative) and the specificity at 92.3% (1 false positive) for detection of lymph node metastasis on primary staging of high-risk PCa patients. Positive and negative predictive value were 75% and 92.3%, respectively; accuracy of the test was calculated at 88.2%. All patients were submitted to 68Ga PSMA PET-CT re-evaluation 6 months after surgery and tested negative for local, nodal, or distant recurrence of disease. 68Ga PSMA PET-CT appears to have a high negative predictive value for local lymph node metastases in high-risk primary PCa when compared to pathologic findings of eLND. Its role in the primary nodal staging of high-risk PCa patients worths further evaluation.