Accuracy of Ga-Prostate-specific Membrane Antigen Positron Emission Tomography for the Detection of Lymph Node Metastases Before Salvage Lymphadenectomy

Imaging modalities with high accuracy are essential for proper selection of patients for salvage lymph node dissection (sLND). Unlike nodal staging before radical prostatectomy, data on prostate-specific membrane antigen (PSMA) positron emission tomography (PET) before sLND are scarce. We analyzed 23 patients undergoing 68Ga-PSMA-PET before sLND and compared the imaging findings with histopathology at sLND. Altogether, 29/109 resected lymph node (LN) fields harbored histologically confirmed LN metastases (26.6%)., The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 89.5%, 74.1%, 70.8%, 90.9%, and 80.4% in side-based analysis, and 75.9%, 87.5%, 68.8%, 90.9%, and 84.4%, respectively, in LN field-based analysis. In contrast to existing studies, sensitivity in particular was lower. This might be because of referral for sLND on the basis of PSMA-PET from 13 different nuclear medicine centers. However, this could still provide more realistic data if sLND should become widely used. Second, our pathologists routinely used immunohistochemistry, resulting in a higher yield of smaller metastases, increasing the accuracy of histopathology. Despite its acceptable accuracy in a real-world scenario, sLND should not only focus on PSMA-PET-positive fields, as small PSMA-PET-negative metastases may be present.

PATIENT SUMMARY: We analyzed the accuracy of prostate-specific membrane antigen positron emission tomography (PSMA-PET) before salvage lymph node dissection in a real-world situation. Although the accuracy is reasonable, resection should not exclusively focus on PSMA-PET-positive fields.