Ga-labeled Prostate-specific Membrane Antigen Ligand-positron-emission Tomography: Still Just the Tip of the Iceberg

OBJECTIVES To assess the performance of Ga-labeled prostate-specific membrane antigen ligand-positron-emission tomography (Ga-PSMA PET) for positive lymph nodes on imaging after curatively intended radical prostatectomy. PATIENTS AND Seventeen patients with biochemical recurrence after radical prostatectomy undergoing robot METHODS assisted salvage lymphadenectomy for positive lymph nodes on imaging were included in this single surgeon study. The performance of Ga-PSMA PET was assessed on per patient, per lesion, per landing site and per laterality level using sensitivity, specificity, and negative and positive predictive value analysis. RESULTS A total of 34 positive nodes were detected on Ga-PSMA PET with a median of 2 nodes per patient (IQR 1-3 nodes per patient). Sixty six nodes were pathologically disease positive from 14 patients, with a median of 2 positive nodes per patient (IQR 1-6). Three patients had no pathologically detectable disease. On a per patient basis, the positive predictive value was 82%. Sensitivity, specificity, and negative predictive value were not able to be calculated as all patients had disease recurrence with a detectable prostate-specific antigen.On a "per lesion" basis, the sensitivity, specificity, positive predictive value, and negative predictive value were 36.7%, 96.9%, 73.5%, and 86.7%, respectively. CONCLUSION Our study indicates that sensitivity of Ga-PSMA PET in the salvage setting is not yet sufficient to detect all sites of metastasis. Therefore, imaging-guided metastasis targeted treatment is likely to fail given the likely concomitant imaging negative more widespread disease. Crown Copyright (C) 2018 Published by Elsevier Inc.